Electrochemical system with confined electrolyte

ABSTRACT

Described herein are systems and methods for the management and control of electrolyte within confined electrochemical cells or groups (e.g. stacks) of connected electrochemical cells, for example, in an electrolyzer. Various embodiments of systems and methods provide for the elimination of parasitic conductive paths between cells, and/or precise passive control of fluid pressures within cells. In some embodiments, a fixed volume of electrolyte is substantially retained within each cell while efficiently collecting and removing produced gases or other products from the cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 62/799,966, filed Feb. 1, 2019, titled “ElectrochemicalSystem with Confined Electrolyte,” and U.S. Provisional PatentApplication 62/854,757, filed May 30, 2019, titled “Water Electrolyzerswith Thermal Management Systems,” each of which is incorporated hereinby reference in its entirety to the extent not inconsistent herewith.

FIELD OF THE INVENTION

This invention generally relates to electrochemical systems and in someembodiments more particularly to cells, stacks, and operations ofelectrochemical cells for producing gaseous products.

BACKGROUND

Hydrogen in molecular form (H₂) has been a valuable commodity for manydecades. Uses typically include ammonia production, catalytic crackingof hydrocarbons and other industrial applications.

It has been recognized that hydrogen can also serve as an energy-storagemedium and will play a role in the future energy economy. One expectedmethod for use of hydrogen in this application is through injection intothe natural gas grid where enormous capacity for the storage of energyin the form of hydrogen gas is already available. This application iscalled Power to Gas (P2G) or Green Hydrogen. As P2G and Green Hydrogentechnologies proliferate, electric power consumed by electrolyzers willincrease.

Existing electrolyzer systems have many shortcomings which result inreduced efficiency and increased system complexity leading to increasedcosts.

SUMMARY

Various embodiments will be described in detail with reference to theaccompanying drawings. References made to particular examples andimplementations are for illustrative purposes and are not intended topreclude the inclusion of other implementations. Various components,sub-systems, and modifications of the various embodiments may bere-combined with components, sub-systems, or modifications of otherembodiments to form further embodiments.

Water electrolysis for the production of hydrogen and other gases iscurrently performed in systems of two types. Polymer electrolytemembrane (or proton exchange membrane, both abbreviated PEM)electrolyzers utilize a solid polymer electrolyte to conduct protonsbetween positive and negative electrodes. Such systems generally involvepumping pure deionized water into a stack of cells, each containing asolid polymer electrolyte. Solid polymer electrolytes are generally verythin, historically allowing for higher current density operation withlow resistance. Additionally, solid polymer electrolyte membranes tendto substantially limit the quantity of gas that crosses from onehalf-cell to the other through the membrane, resulting in higher gaspurity and reduced losses.

However, solid polymer electrolytes also tend to be more resistive toionic conductivity than liquid or gel electrolytes. The higherresistance leads to increased efficiency losses. PEM electrolyzers alsotend to require costly materials such as platinum-group metal catalystsand titanium or gold support structures. As a result, despite theiradvantages, PEM electrolyzers can be quite expensive to build andoperate.

The second type, alkaline electrolyzers, use an aqueous alkalineelectrolyte solution to conduct ions between the electrodes across anelectrically non-conductive separator. Alkaline electrolyzers benefitfrom lower cost materials and may potentially display improvedperformance owing to the highly conductive nature of the electrolyte. Ascompared with PEM electrolyzers, alkaline electrolyzers tend to be lesssusceptible to gas crossover. Nonetheless, alkaline electrolyzers remainsusceptible to other complications. One of the most substantialshortcomings of alkaline electrolyzers is the parasitic losses caused byso-called “shunt currents.”

In conventional state-of-the-art alkaline electrolyzers, the water splitin the electrolysis reaction is the water in the aqueous electrolytesolution which is pumped through a cell stack. Circulating theelectrolyte through the stacks provides various benefits such asexposing the electrodes to a well-mixed electrolyte solution, allowingfor the removal of dissolved gases external to the cells, and allowingfor simple maintenance of hydroxide (or other electrolyte)concentration.

Such alkaline electrolyte systems generally use a manifold or othercommon electrolyte flow channel to direct electrolyte into and throughall cells of a stack. These common channels containing electricallyconductive electrolyte create a conductive path between cells throughwhich electric currents can flow. These “shunt currents” do not supportthe desired electrochemical reactions in the cells, and thereforerepresent a form of inefficiency sometimes referred to as a parasiticloss.

Most approaches to mitigating or eliminating shunt currents tend to beminimally effective, costly, or introduce further system inefficiencies.Nonetheless, the costs and inefficiencies imposed by shunt currents arewidely accepted as the inevitable cost of operating an alkalineelectrolyzer.

Applicants have taken a different approach to avoiding shunt currents,and in the process realized several other advantages. Instead offighting the challenges of a flowing electrolyte system architecture,Applicants have developed an electrochemical cell stack architecturethat eliminates the need for flowing electrolyte through an entire cellstack by integrating functions of the “balance of plant” into each layerof the cell-stack. In such a system, each cell or half-cell contains aquantity of electrolyte that is confined within the cell or half-celland fluidically isolated from electrolyte in any other cells. Theelectrolyte thus confined is not capable of creating unwantedelectrically conductive paths with other cells within the stack. As aresult, parasitic shunt currents are avoided. The avoidance of shuntcurrent provides for benefits unavailable to conventional alkalineelectrolyzers, such as the ability to incorporate more cells within asingle stack than is feasible in conventional alkaline electrolyzers,thereby achieving higher stack voltages and improving overallefficiency. The lack of flowing electrolyte also allows for improved gaspurities by mitigating forces tending to cause gas produced in onehalf-cell to cross over into a counter-half-cell (generally referred toherein as “gas crossover” or simply “crossover”).

Notwithstanding references herein to alkaline electrolysis systems, theskilled artisan will recognize that the devices, systems, and methodsdescribed herein may be applied to a wide range of electrochemical cellsand systems, including various chemical-producing electrolyzers, batterysystems, fuel cell systems, electrochemical systems for purifying water,materials, or chemicals, and other electrochemical cell systems.

The unique architecture described herein comprises several componentsand sub-systems, including an electrolyte confinement system forsubstantially confining aqueous electrolyte within each cell orhalf-cell; an electrolyte capture system for capturing any electrolytethat escapes the confinement system; an electrolyte return system forreturning electrolyte that escapes a cell or half-cell back into thecell or half-cell chamber; a passive pressure-driven water supply systemfor supplying a make-up liquid (e.g., deionized water in someembodiments) to the each cell or half-cell to replace liquid (e.g.,water) consumed in electrochemical reactions within the cell whilesubstantially minimizing pressure differences across the separatormembrane; a high-pressure gas collection system for collecting producedgases at high pressures without requiring external gas compression; anda volume expansion system for accommodating volumetric expansion andcontraction of fluids within a cell.

Some embodiments of the subsystems above may also utilize a unique pumpconfiguration referred to herein as a “ventricular” pump. Embodiments ofelectrochemical systems herein may also be configured to passively butautomatically control various pressure regions and pressure gradientsunder active fluid pressure control at a minimal number of points withinthe system.

In some embodiments, an electrochemical system as described herein maybe operated at a high absolute pressure while maintaining relativepressure-differences between various pressure regions within desiredranges. Operating a gas-producing electrochemical cell at a highabsolute pressure may allow for gases to be produced and delivered athigh pressures without the need (or with a reduced need) for additionalcompressors to pressurize gases to a pressure required by a particularapplication.

In various embodiments, an electrochemical system to be operated at anelevated pressure (i.e., at an absolute pressure greater thanatmospheric pressure) may include a cell-stack and/or other structureswithin one or more pressure vessels or by using a plate-and-frame cellstack arranged to hold the desired degree of pressure relative toatmospheric pressure. In some embodiments, operating at a high absolutepressure may be accomplished by pre-pressurizing one or more cellregions with an inert or minimally-reactive gas (e.g., nitrogen, argon,helium, neon, or various combinations of these or other gases). In otherembodiments, a high operating pressure may be initially establishedand/or maintained by pumping a make-up liquid (e.g., water) into thecell-stack at a desired absolute pressure. For example, in someembodiments, an electrochemical system may be pre-pressurized andoperated at an absolute pressure of about 10 bar, 20 bar, 30 bar, 40bar, 50 bar, 60 bar, 70 bar, 80 bar, 90 bar, 100 bar, 10 atm, 20 atm, 30atm, 40 atm, 50 atm, 60 atm, 70 atm, 80 atm, 90 atm, 100 atm or more.

In an aspect, provided is a stack of confined electrolyteelectrochemical cells, each individual electrochemical cellindependently comprising: a) a first half-cell chamber containing afirst volume of electrolyte in contact with a first electrode; b) asecond half-cell chamber containing a second volume of electrolyte incontact with a counter-electrode; c) a separator separating the firsthalf-cell chamber from the second half-cell chamber; and d) a firstelectrolyte capture-and-return system in communication with the firsthalf-cell, the electrolyte capture-and-return system configured toreceive a captured electrolyte from the first volume of electrolyteescaping the first half-cell chamber and to drive the capturedelectrolyte back into at least one of the first half-cell chamber andthe second half-cell chamber via an electrolyte return conduit. Inembodiments, the capture-and-return systems in an individualelectrochemical cell may be fluidically isolated from capture-and-returnsystems in the other electrochemical cells in the stack. In embodiments,the stack may comprise a bipolar stack comprising bipolar plates joiningadjacent cells.

The electrochemical system may further comprise a second electrolytecapture-and-return system in communication with the second half-cellchamber, the second electrolyte capture-and-return system configured tocapture electrolyte from the second volume of electrolyte escaping thesecond half-cell chamber and to drive the captured electrolyte back intothe first half-cell chamber, the second half-cell chamber or both.

The first and second electrolyte capture-and-return systems may comprisea liquid-gas separation chamber. The liquid-gas separation chamber mayuse gravity to allow for the capture of liquid electrolyte while havinga headspace to allow for the flow of gas, including product gas. Thefirst and second electrolyte capture-and-return systems may be in fluidcommunication with a gas removal manifold and the gas removal manifoldis in fluid communication with each of the electrochemical cells in thestack. The first and second electrolyte capture-and-return systems maycomprise a gas-removal liquid. The gas removal liquid may be maintainedwithin a pre-determined range of fluid pressure.

The electrochemical system may further comprise a fluid escape elementthrough which gas and liquid electrolyte escapes the first half-cellchamber or second half-cell chamber into the first electrolytecapture-and-return system or second electrolyte capture-and-returnsystem, respectively. The fluid escape element may be configured toimpart a resistance to fluid flow. The fluid escape element may beconfigured to impart a non-linear resistance to fluid flow, wherein thefluid comprises both gas and liquid. The fluid escape element maycomprise an egress channel through which a bolus of gas and a bolus ofliquid may only flow in series. A fluid escape element can comprise oneor more egress channels and/or one or more membranes, according toembodiments described herein. In some embodiments, a fluid escapeelement can consist of one or more egress channels and/or one or moremembranes, according to embodiments described herein.

The electrolyte capture-and-return system may comprise an electrolytecapture volume. The electrolyte capture-and-return system may comprise amembrane positioned between said half-cell and said electrolyte capturevolume. The electrolyte capture-and-return system may comprise amembrane to promote the flow of product gas while maintainingelectrolyte in the electrolyte capture-and-return system, for example,positioned between a product gas outlet and the electrolyte capturevolume. The electrolyte capture-and-return system may comprise one ormore pumps configured to return the electrolyte to the first half-cellor the second half-cell. The electrolyte capture-and-return system isconfigured to allow for mixing of the electrolyte, for example, betweenthe two half-cells of an electrochemical cell.

The electrochemical system may be a battery, a flow battery or a fuelcell. The electrochemical system may be an alkaline electrolysis cell.The electrochemical cell generates hydrogen gas and oxygen gas asproduct gasses. The electrolyte may be an aqueous alkaline solution. Theelectrolyte may comprise potassium hydroxide, sodium hydroxide, lithiumhydroxide or any combination thereof.

The electrochemical cell may further comprise an expansion chamber influid communication with the first half-cell and the second half-cell,the expansion chamber being configured to allow volumetric expansion offluid in one or both of the half-cell chambers as gas bubbles in theelectrolyte increase the volume of the mixed fluid. The expansionchamber is configured to reduce pressure gradients between the firsthalf-cell and the second half-cell. The expansion chamber may maintainsubstantially equal pressure in the first half-cell and the secondhalf-cell, for example, a difference in pressure of less than 2 atm,less than 1 atm, less than 0.5 atm or optionally, less than 0.25 atm.The expansion chamber may be in fluid communication with the electrolytecapture-and-return system.

The electrochemical cell may further comprise an expansion resistor inoperable communication with the expansion chamber. The expansionresistor may be a spring, a bellow, a diaphragm, a balloon, a physicalproperty of the expansion chamber or any combination thereof. Theexpansion chamber may comprise a divider to maintain separation of theelectrolyte from the first half-cell and the second half-cell. Such adivider may also be configured to allow fluid pressures in the twohalf-cells to equilibrate. The expansion chamber may impart a resistanceto expansion causing an increase in fluid pressure when the expansionchamber volume exceeds a threshold volume. The expansion chamber mayimpart a resistance to expansion causing fluid pressure to increaselinearly, geometrically, exponentially, stepwise, or otherwise withincreasing expansion chamber volume.

The electrochemical cell further comprises a make-up liquid supply influid communication with the electrochemical cell to provide make-upliquid to the first half-cell, the second half-cell, or both. Theelectrochemical system may further comprise a one-way valve positionedbetween the make-up liquid supply and the electrochemical cell. Themake-up liquid supply may be provided to the electrochemical cell by asupply manifold in fluid communication with each electrochemical cell inthe stack. The one-way valve may regulate the flow of make-up liquidinto the electrochemical cell based on a pressure differential betweenthe supply manifold and the electrochemical cell. The make-up liquid maybe deionized water.

The electrochemical system may further comprise a pump, for example, aventricular pump or a positive displacement pump, operably connected toeach of the electrochemical cells and arranged to drive capturedelectrolyte from the electrolyte capture volume into one or both of thehalf-cell chambers. The pump may be capable of driving both liquid andgas through the electrolyte return channel. The pump may comprise acompressible section of conduit surrounded by an actuation fluid. Eachelectrochemical cell in the stack may comprise at least one compressibleconduit section in a housing volume exterior to the electrochemicalcell. Each half-cell chamber of each electrochemical cell in the stackmay comprise a compressible conduit section in the housing volume. Theactuation fluid may be contained in a continuous housing volumesurrounding compressible conduit sections of all electrochemical cells.

The stack may be arranged in a prismatic layered configuration (e.g., aplate-and-frame configuration), a concentric cylindrical configuration,a spiral jellyroll configuration, a prismatic jellyroll configuration orany other rolled jellyroll configuration.

In an aspect, provided is an electrochemical system comprising: at leastone confined electrolyte electrochemical cell comprising: a) theelectrolyte; b) a first half-cell comprising a first electrode incontact with first portion of the electrolyte and a first electrolytecapture-and-return system; c) a second half-cell comprising a secondelectrode in contact with a second portion of the electrolyte and asecond electrolyte capture-and-return system; and d) a separatorseparating the first half-cell from the second half-cell; wherein thefirst electrolyte capture-and-return system is configured to capture theelectrolyte displaced from the first half-cell and return at least aportion of the displaced electrolyte to the first half-cell withoutmixing with electrolyte from any other cell; and wherein the secondelectrolyte capture-and-return system is configured to captureelectrolyte displaced from the second half-cell and return at least aportion of the displaced electrolyte to the second half-cell withoutmixing with electrolyte from any other cell.

The first electrolyte capture-and-return system may be fluidicallyisolated from the second half-cell and wherein the second electrolytecapture-and-return system may be fluidically isolated from the firsthalf-cell.

In an aspect, provided is a method of generating at least one productgas comprising: i) providing an electrochemical system comprising: atleast one electrochemical cell comprising: a) an electrolyte; b) a firsthalf-cell having a first electrode in communication with first portionof the electrolyte and a first electrolyte capture-and-return system; c)a second half-cell including a second electrode in communication with asecond portion of the electrolyte and a second electrolytecapture-and-return system; and d) a separator separating the firsthalf-cell from the second half-cell; ii) capturing at least a portion ofelectrolyte displaced from the first half-cell via a first electrolytecapture-and-return system and returning the captured electrolyte to thefirst half-cell; iii) capturing at least a portion of electrolytedisplaced from the second half-cell via a second electrolytecapture-and-return system and returning the captured electrolyte to thesecond half-cell; and iv) reacting the electrolyte in the at least oneelectrochemical cell thereby generating at least one product gas.

In an aspect, provided is a method for generating hydrogen and oxygengas comprising: i) providing an electrolyzer comprising: a plurality ofelectrochemical cells each independently comprising: a) an aqueouselectrolyte; b) a first half-cell having a first electrode incommunication with first portion of the aqueous electrolyte, a firstelectrolyte capture-and-return system and an oxygen gas capture system;c) a second half-cell including a second electrode in communication witha second portion of the aqueous electrolyte and a second electrolytecapture-and-return system and a hydrogen gas capture system; and d) aseparator separating the first half-cell from the second half-cell ii)capturing at least a portion of electrolyte displaced from the firsthalf-cell via a first electrolyte capture-and-return system andreturning the captured electrolyte to the first half-cell; iii)capturing at least a portion of electrolyte displaced from the secondhalf-cell via a second electrolyte capture-and-return system andreturning the captured electrolyte to the second half-cell; and iv)electrolyzing the aqueous electrolyte in each of the electrochemicalcells, thereby generating hydrogen and oxygen gas, wherein each oxygengas capture system is in fluid communication with one another and eachhydrogen gas capture system is in fluid communication with one another.In some aspects, the capture-and-return systems may be configured tocapture 80%, 90%, 95%, 99%, 99.9%, 99.99% or between 99% and 100% (%mass or % volume) of the electrolyte displaced from either half-cell inliquid form and/or in the form of mist and to return at least thecaptured electrolyte to the cell or half-cell from which it wascaptured.

The first electrolyte capture-and-return system may be in fluidcommunication with the second electrolyte capture-and-return system ineach of the electrochemical cells. The first electrolytecapture-and-return system and the second electrolyte capture-and-returnsystem may be associated with an individual electrochemical cell andfluidically isolated from electrolyte capture-and-return systems ofother electrochemical cells in the electrolyzer.

A person having skill in the art will recognize that the variousembodiments and features described as an electrochemical system may beintegrated with the various methods, electrolyzers and other systemsdescribed herein.

In an aspect, provided is a ventricular pump comprising: a) a housingchamber containing an actuation fluid; b) a plurality of conduits, eachextending through a portion of the housing, each conduit comprising acompressible region located within the housing and surrounded by theactuation fluid; each conduit having an upstream one-way valve locatedupstream of the compressible region, and a downstream one-way valvelocated downstream of the compressible region; c) an actuator incommunication with the housing chamber; wherein the actuator isconfigured to apply a compressive and/or expansive force to theactuation fluid sufficient to at least partially compress thecompressible regions of the conduits.

The actuation fluid may be an incompressible liquid or a compressiblegas. Some or all of the upstream one-way valves and some or all of thedownstream one-way valves may be located outside the housing chamber.Some or all of the upstream one-way valves and some or all of thedownstream one-way valves may be located inside the housing chamber.

Some or all of the compressible regions of the conduits may comprise asection of compressible tubing. The electrochemical systems and methodsdescribed herein may use some or all of the electrolyte return conduitsas the conduit of the ventricular pump as described herein. Theventricular pump housing may comprise a portion of an electrochemicalstack housing.

The housing chamber may comprise a plurality of apertures in layers of astacked plate-and-frame cell-stack structure. The ventricular pump mayfurther comprise a compressible conduit section positioned within oradjacent to the housing configured to allow an actuation fluid withinthe housing chamber to drive fluid within the compressible conduitsection.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description sets forth illustrative embodimentswith reference to the accompanying drawings, of which:

FIG. 1 is a schematic illustration of an electrochemical system with acell-specific electrolyte capture and return system.

FIG. 2 is a schematic illustration of an electrochemical system withcell-specific electrolyte capture and return and volume expansionsystems.

FIG. 3A is a schematic conceptual illustration of a ventricular pump.

FIG. 3B is a schematic exploded perspective view of an exampleventricular pump implemented in a planar substrate such as a cell-framestructure.

FIG. 3C is a cross-sectional view illustration of the exampleventricular pump of FIG. 3B.

FIG. 4 is a schematic illustration of an electrolyzer system utilizing astack of FIG. 5A-FIG. 5D are schematic charts illustrating fluidpressure, flow, and volume relationships during various stages ofoperation of an electrolyzer with electrolyte confinement features.

FIG. 6 is a schematic illustration of an electrochemical system in whichmake-up liquid may be passively delivered into the cell without exitingthe cell.

FIG. 7 is a schematic illustration of an electrochemical system in whichmake-up liquid is passively delivered into an inter-electrode spacebetween positive and negative electrodes.

FIG. 8 is a schematic illustration of an electrochemical systemconfigured to be cooled by flowing gases, including gases produced byelectrochemical reactions within the cells.

FIG. 9 is a schematic illustration of an electrochemical systemcomprising electrolyte confinement features and in which one half-cellis flooded with electrolyte and/or make-up liquid and a counterhalf-cell contains only gas, including gas produced in the counterhalf-cell and gas driven through the counter half-cell chamber.

FIG. 10 is a schematic illustration of a gas-cooled PEM (proton exchangemembrane) or AEM (anion exchange membrane) electrochemical cellutilizing electrolyte confinement features.

FIG. 11 is an exploded view illustration of example embodimentcomponents of an electrochemical cell in a plate-and-frame cell-stack.

FIG. 12A is a plan-view illustration showing an example arrangement ofelectrolyte confinement features on a first side of a planar cell-frameconfigured for inclusion in a bipolar plate-and-frame cell-stack.

FIG. 12B is a plan-view illustration showing an example arrangement ofelectrolyte confinement features on a second side of the planarcell-frame of FIG. 12.

FIG. 13 is a cross-sectional illustration of expansion volumesintegrated into cell-frames of two adjacent cells in a cell-stack, takenthrough line X-X shown in FIG. 12A.

FIG. 14A and FIG. 14B are schematic illustrations of exemplaryembodiments of electrolyzer systems with thermal management componentsindependent of process water components.

FIG. 15 is a schematic exploded view illustration of an exemplarymulti-layer cooling bipolar plate with a coolant conduit through whichcoolant may be circulated, according to certain embodiments.

FIG. 16 is a schematic illustration of some features of anelectrochemical cell in an exemplary low-flow PEM electrolyzer,according to certain embodiments.

FIG. 17 is a schematic illustration of some features of anelectrochemical cell in an exemplary low-flow AEM electrolyzer,according to certain embodiments.

FIG. 18 is a schematic illustration of some features of an LFIEelectrolyzer, according to certain embodiments.

FIG. 19 is a block diagram schematically illustrating components of acomputer or electronic controller which may be used to automaticallyexecute methods and processes described herein to control operation ofan electrochemical system.

DETAILED DESCRIPTION

Principles, embodiments and examples of each of these sub-systems willbe described in detail below with reference to the drawings, whichschematically illustrate various examples of electrochemical systemsexhibiting confined electrolyte features and components. The drawingscomprise schematic projections in the sense that they illustratecomponents in ways intended to promote understanding and description,despite the fact that many actual implementations of such systems willtypically utilize very different relative orientations, scales, andpositions of various components.

For example, the relative size and orientations of various illustratedcomponents do not necessarily correlate with actual sizes ororientations of such components in real physical implementations of suchsystems. As a specific example, FIG. 1 shows all components of a cell100 in a common cross-sectional plane, including cell electrodes 102,104, separator 106, electrolyte capture volumes 110, 112, electrolytereturn channels 114, 116, and gas removal manifolds 122, 124. Anyelectrolyte capture volume can be interchangeably referred to herein asan electrolyte collection volume. In some actual implementations, thecell's separator 106 and electrodes 102, 104 may be oriented at a rightangle to the illustrated orientation such that their two-dimensionalsurfaces lie in planes parallel to the illustrated cross-sections. Manydifferent orientations and arrangements are possible, including theexample arrangement described herein with reference to FIG. 12 and FIG.13, among many other possible arrangements.

In a cell-stack based on the system of FIG. 1, each cell in thecell-stack may include half-cell chambers 142, 132, a separator 106,electrodes 102, 104, fluid escape elements 160, 162, 164, electrolytecollection volumes 110, 112, gas collection volumes 186, 188,electrolyte return conduits 114, 116. The supply manifold 178 and thegas-removal manifolds 122, 124 may be joined to all other cells in thestack and to additional processing equipment, for example as describedherein with reference to FIG. 4. In some embodiments, fluid flows in theelectrolyte return conduits 114, 116 may be driven by a single pumpactuator (e.g., ventricular pump actuator) joined to return conduits inseveral (or all) cells of a cell-stack.

Definitions of Terms Used

As used herein, the term “cell” or “full-cell” refers to anelectrochemical unit in which an anode electrode is connected to acathode electrode by an ionically-conductive pathway (e.g., a liquidelectrolyte, salt bridge, solid polymer electrolyte or other pathway forionic conductivity). A cell may be electrolytic (driven by a voltageand/or current applied across the electrodes) or galvanic (in whichspontaneous reactions produce a voltage difference between theelectrodes which may drive an electrical current through an externalelectrical circuit).

As used herein, the term “half-cell” may refer to a single electrode ofa cell (either cathode or anode) or structures associated with that oneelectrode. Because a full cell requires two electrodes interacting withone another electrochemically, an electrode interacting with anidentified half-cell may be referred to as a “counter electrode” or a“counter half-cell” with respect to the first identified half-cell. Thevoltage of a half-cell may be measured relative to a “referenceelectrode” thereby providing a “half-cell voltage.” A full-cell voltageis the (typically absolute value) sum of half-cell voltages of bothhalf-cell electrodes of a full cell.

Generally, an electrochemical cell comprises a first half-cell and asecond half-cell, wherein the first half-cell comprises a firstelectrode and the second half-cell comprises a second electrode, thesecond electrode being at a different potential with respect to thefirst electrode. Generally, an opposite polarity reaction occurs in onehalf-cell compared to the other half-cell. For example, during operationof the electrochemical cell, oxidation (or, reduction) occurs in thefirst half-cell and reduction (or, oxidation, respectively) occurs inthe second half-cell. For example, during operation of theelectrochemical cell, current flows into the first electrode of thefirst half-cell and current flows out of the second electrode of thesecond half-cell, or vice versa, when the first and second electrodesare in direct or indirect electrical communication with each otherduring the electrochemical cell's operation.

A “half-cell chamber” is a chamber or volume and/or structurescomprising a half-cell or electrode thereof. For example, a firsthalf-cell chamber may contain a first electrode (or at least a portionthereof, such as a surface of the first electrode), optionally anelectrolyte, optionally a reactant species (such as reactant gas orliquid), and optionally a produced species (such as a produced gas), andoptionally other structures such as compliant conductive gas egresslayers, flow channels, or other structures. For example, a wall orvolume-confining surface of a half-cell chamber can be a surface of anelectrode, a bipolar plate, a cell-frame, or other structures. Aboundary of a half-cell chamber can fully or partially correspond to aphysical boundary, such as a physical surface of a physical object. Aboundary of a half-cell chamber can fully or partially correspond to anon-physical boundary, such as a space, plane, imaginary surface, orposition between the half-cell chamber and another chamber, volume,structure, or conduit. Typically, but not necessarily, two half-cellchambers (e.g., corresponding to an anode and a cathode) of a full cellare separated by a separator. Typically, any two half-cell chambers havemutually exclusive volumes (not overlapping volumes) with respect toeach other.

As used herein, the term “fluid” refers to matter in a state capable offlow. Fluid may include liquid-only, gas-only, or mixtures of gas andliquid. In some cases, fluid may also include highly viscous liquids or“gel” materials. As used herein, “gas” refers to any material in agaseous phase of matter under the pressure and temperature conditionsobtaining in the system being described. For example, “gas” may includeoxygen gas (O₂), hydrogen gas (H₂), chlorine gas (Cl₂), water vapor, orother gases or gas mixtures.

As used herein, two or more regions referred to as being in “fluidcommunication” with one another indicates a pathway by which fluid maytravel between the regions. Such pathways may include channels, tubes,membranes, conduits, volumes, pipes, hoses, or other structures throughwhich fluid (liquid and/or gas) may transport or be transported, such asby advection, convection, buoyancy, diffusion, flow, or other fluidtransport mechanism. Unless otherwise specified, the term “fluidcommunication” may also include fluid pathways through which flow may beselectively or intermittently interrupted by a valve, or otherstructure. Regions in fluid communication can be in direct fluidcommunication or in indirect fluid communication. Two regions inindirect fluid communication may include intermediate pathways orstructures through which a fluid may flow between the two regions. Theterm “fluidically connected” is also used herein to refer to regionsthat are in fluid communication.

As used herein, the term “electrolyte” may generally refer to any liquidor liquid-like substance (e.g., flowable gels) present in one or bothhalf-cells of an electrochemical cell. Therefore, “electrolyte” mayinclude alkaline electrolytes, acidic electrolytes, solutions containingreactants such as brine or seawater, deionized water, or other liquidsor solutions. Example alkaline electrolytes may include aqueous alkalinesolutions such as potassium hydroxide, sodium hydroxide, lithiumhydroxide, or combinations thereof. Example acidic electrolytes mayinclude acidic aqueous solutions such as hydrochloric acid, sulphuricacid, or others. Some electrolytes may comprise neutral pH aqueoussolutions such as un-purified water, purified water, deionized water, orhighly purified and/or deionized water. Electrolytes may also includeionic liquids, molten salts, or others.

The choice of electrolyte for a particular electrochemical system may bebased on other system components. For example, if a separator membranecomprising an ionomer layer (also known as a “solid electrolyte” layer)is chosen, then the electrolyte may comprise substantially only purifiedand/or deionized water (although in some embodiments, some ionomer layermembranes, such as AEMs, may also be used with an alkaline or acidicelectrolyte). If a separator membrane comprises a porous polymer,ceramic, or other membrane, then the electrolyte will typically comprisean alkaline or acidic solution. In the various embodiments describedherein, the term “electrolyte” is used generically to encompass all ofthese configurations, unless otherwise specified.

As used herein, the term “make-up liquid” may include any liquidconsumed in electrochemical reactions within an electrochemical cellsuch as those described herein. As the term suggests, in manyembodiments make-up liquid is supplied to an electrochemical cell tomake up for (i.e., replace) liquid consumed in the electrochemicalreactions in that cell. In many cases, a make-up liquid may comprisewater, such as high purity deionized water or less pure water. In someembodiments, a make-up liquid may include an electrolyte solution, whichmay be the same electrolyte used in other parts of the cell or anelectrolyte solution with a different composition. In furtherembodiments, a make-up liquid may comprise other mixtures (aqueous ornon-aqueous) of liquids, at least some components of which are expectedto be consumed in the electrochemical cells.

As used herein, the term “deionized water” may refer to water that hasbeen treated to remove at least solid particulates, dissolved orentrained (as bubbles) gases and dissolved ions. Deionized water may bedeionized to varying degrees, which may be measured or reported in termsof electrical conductivity (or resistivity). Fully deionized water istypically reported as having an electrical resistance of over 18megaohm-cm, or a conductivity of less than about 0.05555 microsiemen/cm.“Ultrapure” water typically refers to water with an electricalresistance of at least 1 megaohm-cm (or a conductivity of less than 1microsiemen/cm). These measures are typically made at 25° C., astemperature has a strong influence on electrical conductivity (andresistance). Deionized water described for use in any aspects of systemsand methods herein may have a conductivity (at 25° C.) of less thanabout 20 microsiemen/cm. In some embodiments or uses, deionized waterhaving a conductivity less than about 1 microsiemen/cm or less thanabout 0.06 microsiemen/cm may be used. Some embodiments or uses may usetheoretically “pure” water having a conductivity of about 0.055microsiemen/cm.

As used herein, the term “separator” or “separator membrane” may referto any structure positioned between a positive electrode and a negativeelectrode of a common electrochemical cell and performing the functionof creating an electrically non-conductive separation between thepositive and negative electrodes while allowing ionic conductivitybetween the positive and negative electrodes. Separators may includeopen-structured spacers creating substantially zero ionic resistance orminimal resistance to ionic diffusion, or structures creating greaterresistance to ionic diffusion such as porous, microporous, ornano-porous membranes (e.g., polymer membranes), gels, beads, solidelectrically insulative and ion-conducting sheets (e.g., ionomers,“solid electrolyte” membranes, proton-exchange membranes, or anionexchange membranes), ceramics, or other structures or materials asdescribed in further detail and examples herein. In some embodiments,the term “PEM separator” refers to a separator comprising aproton-exchange membrane (PEM) ionomer layer alone or in combinationwith other layers. In some embodiments, the term “AEM separator” refersto a separator comprising an anion-exchange membrane (AEM) ionomer layeralone or in combination with other layers.

As used herein, the term “liquid-gas separator” may refer to one or morestructures capable of dividing a liquid-gas mixture into separate liquidand gas streams. Various example liquid-gas separator structures areshown and described herein below.

As used herein, the term “passive control” refers to control methods andmechanisms that do not rely on electronic controllers, sensors,electronically controlled actuators, electric motors or pumps (or othercontrol) and that do not consume energy. “Passive” control methods anddevices typically involve the use of self-managing feedback loopscomprising materials or devices with particular properties, such asdamping properties, deformation properties, resilience properties, orothers. Passive control contrasts with “active” control methods asdefined herein, which typically involve sensors that monitor systemstate or changes in state (e.g., temperature, pressure, pH, etc.) and/orpowered actuators that maintain system conditions under control of anelectronic controller. Such active control methods consume energy andare therefore parasitic in character when considering the energyconsumption of the system as a whole.

“Capture-and-return system” refers to a system (including conduits,chambers, devices, membranes, elements, etc.) configured to collectelectrolyte exiting a half-cell chamber and return it into the half-cellchamber and/or a counter-electrode half-cell chamber of the same cell.In an embodiment, for example, the capture-and-return system comprisesan electrolyte collection volume (110, 112) and a gas separation volume(182, 184) to facilitate separation of product gas and electrolyte thathas escaped the half-cell. The capture-and-return system may alsocomprise an electrolyte return conduit arranged and configured to returncaptured electrolyte into one or both half-cell chambers of the cellfrom which the electrolyte escaped, and an isolated a pump or pumpcomponent arranged and configured to drive the captured electrolytethrough the electrolyte return conduit without mixing with electrolytefrom any other cell of the stack. Various other useful components may beincluded in or used in conjunction with the capture-and-return systemand described herein.

Cell regions, structures, or volumes may be referred to herein as being“fluidically isolated” from one or more other regions, structures, orvolumes in the same cell or different cells. In such usage, the term“fluidically isolated” refers to those regions, structures, or volumesas being separated by one or more permanent, non-permeable fluidbarriers that prevent direct fluid (gas and/or liquid) flow betweenthose structures. Similarly, two or more regions, structures, or volumesmay be referred to as being “electrically isolated” from one another,indicating that one or more electrically non-conductive (or electricallyinsulative) material or structure prevents electrical current fromflowing from one to the other. In some embodiments, a capture-and-returnsystem of a first cell or half-cell may be fluidically and/orelectrically isolated from capture-and-return systems of other cellseven if gas collected from the first cell or half-cell is merged withgas collected from the other cells or half-cells and even if make-upwater is delivered to the cells or half-cells from a common supply. Insome embodiments, electrolyte return systems of two or more cells orhalf-cells may be fluidically isolated from one another even if commonpumping or actuation fluid drives ventricular pumps in both cells orhalf-cells. A system may also be fluidically isolated from other cellswhile allowing for electrical communication between cells (e.g., bipolarconnections) or stacks (e.g., series or parallel electrical connectionsbetween stacks). When two regions are fluidically isolated from eachother they are not in fluid communication with each other.

“Contact” refers to any operational communication between theelectrolyte and an electrode including, for example, physicalcommunication, chemical communication, electrochemical communication,and/or ionic communication, etc. For example, contact may refer to ioniccommunication between an electrode and electrolyte so that theelectrolyte is capable of reacting chemically or electrochemically withspecies, catalysts, or structures in the electrode. An electrolyte maybe in contact with multiple electrodes. The electrode may be partiallyor fully submerged in the electrolyte or ions present in the electrolytemay be conducted through a separator (e.g. a wetted or gelled separatoror other wetted/wicking structure, a solid ionomer or otherion-conducting structures). Contact between an electrode and anelectrolyte may involve one or more intermediate structures such as aninterfacial layer or material such as an oxide layer or solidelectrolyte interface layer.

“Stack” or “cell-stack” as used herein refers to any grouping of aplurality of electrochemical cells in an electrical, physical, and/orlogical structure. Stack may refer to any physical geometry orconfiguration. For example, stack may refer to electrochemical cellsconnected in series, in parallel or in more complex configurations.Individual electrochemical cells within a stack may be arranged in aprismatic layered configuration, a concentric cylindrical configuration,a wound “jellyroll” configuration (spiral, prismatic, or otherwiserolled), or others. Nonetheless, the benefits of confining electrolyteto each cell are most beneficial in a series-connected bipolarcell-stack configuration. A cell-stack may be configured in afilter-press configuration, also referred to as a “plate-and-frame”configuration made up of multiple layers stacked together and comprisingmanifolds for delivering fluids to and removing fluids from eachindividual cell within the cell-stack.

A group of electrolysis cells may be arranged in a cell-stack in abipolar configuration in which adjacent electrochemical cells areelectrically joined in series via a conductive bipolar plate that isimpermeable to both liquid and gas. Each bipolar plate has a positivecharge on one side associated with a positive half-cell of a first celland a negative charge on the opposite face associated with a negativehalf-cell of an immediately adjacent cell.

As used herein, the term “manifold” generally refers to a fluid-carryingchannel that extends through a cell-stack and is common to allindividual cells of a cell-stack. Manifolds or features described as“common” to all cells of a cell-stack may deliver fluid to or removefluid from each of the cells. Common manifolds are in fluidcommunication with each cell in a fluidic parallel arrangement. Oneprincipal benefit of the confined-electrolyte systems described hereinis that common manifolds containing electrically conductive fluids arebroadly eliminated, thereby eliminating pathways for parasitic shuntcurrents.

As used herein, some features or structures are described as being“unique to” a particular cell or half-cell, or each cell (or half-cell)in a stack may be referred to as having a feature “unique to” each cell.A structure or feature identified as “unique to” a cell or half-cell isa structure or feature that may only interact with other structures orfeatures of that respective cell or half-cell, respectively, withoutinteracting with any structure, feature, gas or liquid from any othercells or half-cells.

As used herein, “consumption” of water, or water that is “consumed,”refers to electrochemical, electrolytic, conversion or splitting of thewater into hydrogen gas and oxygen gas. For example, a rate at whichwater, such as process water, is consumed in a cell refers to the rateat which the water is electrochemically converted, or split, intohydrogen gas and oxygen gas in the cell. The rate of water consumptionin a cell depends factors including, but not limited to, temperatureassociated with the cell (e.g., the temperature of process water,electrode temperatures, and/or other solid cell components), pressureassociated with the cell (such as a fluid pressure in one or bothchambers of the cell), and/or electrical current applied to the cell andthe availability of electrode reaction sites sufficiently wetted withprocess water to allow electrochemical reactions to occur efficiently.

The term “ion-exchange electrolyzer” is used herein as a generic termencompassing electrolyzers utilizing solid-polymer electrolyte membranesconfigured to exchange anions and/or cations (including protons).Therefore, the term “ion-exchange electrolyzer” includes electrolyzersutilizing a PEM (proton exchange membrane) (also known as a cationexchange membrane, abbreviated CEM), an AEM (anion exchange membrane),or other membrane comprising, consisting of or consisting essentially ofan ionomer material. Such membranes may be made as independentfree-standing structures (e.g., a sheet of material) or may beintegrated with a positive or negative electrode such as by coating oneor more electrode surfaces with one or more layers of ionomer (andoptionally other polymers) to form a membrane-electrode assembly (MEA).

“Ionomers” are generally defined as polymers made up of alternatingrepeat units of electrically neutral units and ionized units covalentlybonded to a polymer backbone. Such ionized units are often carboxylicacid groups. Depending on the nature of the ionic groups chemicallyattached to a polymer backbone, ionic polymers (ionomers) may be dividedinto cationomers, anionomers, and ampholytes which contain both cationicand anionic groups. Although relatively few ionomer membranes areavailable commercially, a wide range of ionomer materials have beenstudied as described, for example in “Ionomers; Synthesis, Structure,Properties and Applications” edited by M. R. Tant, K. A. Mauritz, and G.L. Wilkes (1997, ISBN-13: 978-0751403923). Example ionomers includeethylene acrylic acid copolymer (EAA), sold under the tradenames SURLYN®and NUCREL®, by DuPont®.

Example PEM materials include sulfonated tetrafluoroethylene-basedfluoropolymer-copolymers (e.g., perfluorosulfonic acid or PFSA) such asthe category of membranes from DUPONT® known by the trademark NAFION®.Example AEM membranes include various membranes sold by DioxideMaterials under the trademark SUSTANION®. The company FUMATECH BWT GmbHalso sells various ionomer membranes under the trademarks FUMAPEM®, andFUMASEP®, FUMION®, and FUMEA®, any of which may be used in anion-exchange electrolyzer as described herein. Membranes comprising anyother PEM, AEM or other ionomer materials may also be used inion-exchange electrolyzers as described herein.

References herein to catalysts, such as hydrogen evolution catalysts,oxygen evolution catalysts, or others, are intended to include anycatalyst known to be capable of catalyzing the identified reaction, andmay include platinum-group metals, precious metals, noble metals, basemetals, alloys of two or more metals, high-surface-area carbon,high-surface area metal or metal alloy structures, conductive polymers,or other materials demonstrated to catalyze a desired electrochemical orchemical reaction.

In various embodiments, the architecture, systems, and methods describedherein may be applied to various electrochemical systems and processes.For example, in some embodiments, an electrochemical system havingfeatures described herein may be an alkaline electrolyzer system inwhich an aqueous alkaline hydroxide electrolyte (e.g., potassiumhydroxide, sodium hydroxide, lithium hydroxide, or combinations thereof)is used to split water in the electrolyte into hydrogen gas at thenegative electrode and oxygen gas at the positive electrode. In otherembodiments, electrochemical systems as described herein may use otherliquid electrolytes, such as acidic aqueous solutions, neutral pHaqueous solutions, ionic liquids, molten salts, or others.

Although some embodiments herein are described with reference to systemsoptimized for electrolytic splitting of water into hydrogen and oxygengases, the various systems, methods, structures, and embodimentsdescribed herein may also be applied to other electrochemical systemssharing structural or functional similarities with the systems describedherein.

Introduction to Confined Electrolyte System Components & Concepts

FIG. 1 schematically illustrates one cell and other components of anelectrolyzer system configured to confine electrolyte to a cell 100. Theillustrated cell 100 includes a positive electrode 104 and a negativeelectrode 102 spaced from one another by a separator 106. The positiveelectrode 104 is shown within a positive half-cell chamber 132 with avolume of positive electrolyte 131 submerging the positive electrode 104and a positive gas headspace 134 shown above a level 136 of theelectrolyte 131. Similarly, the negative electrode 102 is shown in anegative half-cell chamber 142 which contains a volume of negativeelectrolyte 130 submerging the negative electrode 102 and a negative gasheadspace 144 is shown above the level 146 of the electrolyte 130. Aswill be described in various embodiments herein, a gas headspace may ormay not be present in one or both half-cell chambers.

In some embodiments, a headspace divider 150 may be present to separatea headspace into separate positive headspace 134 (headspace of thepositive-polarity half-cell) and negative headspace 144 (headspace ofthe negative-polarity half-cell) regions, thereby preventing gasesproduced by the electrodes 104, 102 from mixing. In various embodiments,the separator 106 or other cell components may also be configured tominimize or prevent gas crossover from one half-cell chamber to theother.

In some embodiments, the negative headspace region 144 may be incommunication with a negative gas removal manifold 122, and the positiveheadspace region 134 may be in communication with a positive gas removalmanifold 124. In some embodiments, one or both gas removal manifolds122, 124 may contain a gas-removal liquid 152.

In various embodiments, one or more fluid escape elements 160, 162, 164may provide a pathway between each half-cell chamber 132, 142 and acorresponding gas removal manifold 124, 122. Such fluid escape elements160, 162, 164 may be configured to allow the escape of gas from thehalf-cell chamber 132, 142 while substantially limiting a quantity ofliquid electrolyte 130, 131 that escapes from the half-cell chamber 132,142. In some embodiments, the fluid escape element may also beconfigured to maintain a desired pressure differential between arespective half-cell chamber and a corresponding gas removal manifold.For example, various gas escape elements may be configured to maintain apressure differential of about 0.01 mbar to about 1 bar or more. FIG. 1illustrates multiple fluid escape element structures and locations, thedetails of which will be further described herein below.

In some embodiments, the negative half-cell chamber 142 and the positivehalf-cell chamber 132 may also be in communication with respectiveelectrolyte collection volume 110, 112. Each electrolyte collectionvolume 110, 112 may be in fluid communication with a respectiveelectrolyte return conduit 114, 116 which may return electrolyte to therespective half-cell chamber under the force of one or more pumps 172,174.

FIG. 1 also illustrates a supply inlet 176 configured to deliver make-upliquid from a supply manifold 178 to the cell 100 to replace liquidconsumed or otherwise removed from the cell, including liquid that isconsumed by being converted to one or more gases at the electrodes 102,104 and removed from the cell via the gas removal manifolds 122, 124.Make-up liquid may also replace liquid removed from the cell in vaporform (e.g., water vapor). In the case of a water electrolyzer system forproducing hydrogen from water, the make-up liquid may be substantiallypure water, such as deionized water or other water of sufficient purityfor a particular application. In other embodiments, the make-up liquidmay comprise some quantity of an electrolyte liquid or other liquidmixed with water.

In various embodiments, an electrochemical system containing featuresand advantages as described herein may be constructed in monopolar orbipolar stack configurations. In some embodiments, features andsub-systems described herein may be integrated into individual layersand cells within a cell stack. In some embodiments, some features orsubsystems may be integrated into a stack, while others may be providedexternal to a stack. Example monopolar and bipolar stack configurationsare described on pages 33-39 of the publication entitled“Pre-investigation of Water Electrolysis, PSO-F&U 2006-1-6287, Draft04-02-2008” by J. O. Jensen, V. Bandur. N. J. Bjerrum, S. H. Jensen, S.Ebbesen, M. Mogensen, N. Trophoj, L. Yde, of the Technical University ofDenmark and the Danish RISO, which is referred to herein as the “JensenReport.”

Water electrolyzers traditionally have been grouped in twoclassifications—unipolar and bipolar. In unipolar electrolyzers,electrodes of the same polarity are electrically connected to oneanother in parallel. The oldest form of industrial electrolysis of wateruses the tank electrolyzer in which a series of electrodes, anodes andcathodes alternately, are suspended vertically and parallel to oneanother in a tank partially filled with electrolyte. Alternateelectrodes, usually cathodes, are surrounded by diaphragms that preventthe passage of gas from one electrode compartment to another. Thediaphragm is impermeable to gas, but permeable to the cell'selectrolyte. The whole assembly is hung from a series of gas collectors.A single tank-type cell usually contains a number of electrodes, and allelectrodes of the same polarity are connected in parallel, electrically.

In bipolar electrolyzers, electrodes are connected to one another inelectrical series. Electrolyzers of the bipolar design may comprise asingle massive assembly of a relatively large number of electrodes, eachof which is cathodic on one side and anodic on the other. More recentelectrolyzer designs use stacks so that the positive electrode of onecell is directly connected to the negative electrode of the next. Abipolar assembly of cells has superficial resemblance to a filter pressbecause the electrolyte is manifolded to flow through each cell inparallel while hydrogen and oxygen exit lines are similarly manifoldedthrough the stack. The assembly is held together by a number of heavylongitudinal tie bolts, in a manner similar to that of the plate-andframe filter press. Each electrode is insulated from, and electricallyin series with its neighbor; and each pair of electrodes, withseparating diaphragm, forms an individual cell unit. In practice,filter-press-type cells are usually constructed with separate electrodesin each cell that are electrically connected through a solid metal (orother conductive material) separator plate (a “bipolar plate”) thatserves as an electrical conductor while keeping the hydrogen cavity ofone cell separate from the oxygen cavity of the next. The direction ofcurrent flow is from one end of the “cell-stack” to the other. A bipolarelectrolyser may thus contain from ten to several hundred individualcells in series. Because the cells of the filter-press-type electrolyzercan be relatively thin, a large gas output can be achieved from arelatively small piece of equipment.

In some embodiments as shown in FIG. 2, the electrolyte return conduits114, 116 may also be in fluid communication with an expansion volume 280configured to allow volume expansion of the contents of one or bothhalf-cell chambers. In some embodiments, a fluid conduit may allow fluidcommunication between the positive electrolyte 131 and the negativeelectrolyte 130 at a location other than an expansion volume 280. Someexample cell configurations with other electrolyte fluid communicationregions are described herein with reference to FIG. 6-FIG. 9.

In a cell-stack based on the system of FIG. 2, each cell in thecell-stack may include half-cell chambers 242, 232, a separator 206,electrodes 202, 204, fluid escape elements 260, 261, electrolyte capturevolumes 210, 212, electrolyte return conduits 214, 216, gas collectionvolumes 286, 288, and expansion volume 280. The supply manifold 278 andthe gas-removal manifolds 222, 224 may be joined to all other cells inthe stack and to additional processing equipment, for example asdescribed herein with reference to FIG. 4. In some embodiments, fluidflows in the electrolyte return conduits 214, 216 may be driven by asingle pump actuator (e.g., ventricular pump actuator) joined to returnconduits in several (or all) cells of a cell-stack.

In various embodiments, an electrochemical system as described hereinmay be configured to automatically manage pressure relationships betweenvarious pressure regions. Cross-separator pressure differences tendingto drive gas crossover can be minimized by maintaining and managingthese various pressure regions. These pressure regions include a make-upliquid supply manifold, half-cell chambers, gas separation volumes, andgas removal manifolds. In various embodiments, these pressure regionsmay be maintained actively by closed-loop electronic controllersoperating based on sensor input, or passively by structures with innateproperties that will tend to dampen rapid pressure oscillations and/orstructures that will perform a desired operation in response to a systemcondition.

Embodiments of an electrochemical system as described herein may beconfigured such that pressure in cell is increased by gas-generationreactions, and pressures in gas removal manifolds and a make-up liquidsupply manifold may be independently controlled by one or more activecontrollers. As will be further described below, the half-cell chambersmay be configured to resist flow of fluids leaving the half-cell, andsuch flow resistance may dampen the effect of pressure variations incontrolled gas removal manifolds on the half-cell pressures.

Electrolyte Confinement System

The electrolyte confinement system generally comprises features andstructures configured to retain the vast majority of electrolyte withineach cell or half-cell chamber while allowing produced gas to escape thecell or half-cell chamber. Some features of the electrolyte confinementsystem may be configured to allow gas and electrolyte to escape a cellor half-cell chamber in a pressure-balanced manner that produces aminimal pressure differential across a cell separator.

As used herein, the term “cross-separator pressure differential” refersto a difference in fluid pressure between two half-cell chambers of acommon cell, typically (but not necessarily) divided by a separator. Asdescribed herein, many cell configurations may include a separatormembrane dividing a cell into half-cells and creating an electricallynon-conductive separation between positive and negative electrodes ofthe cell. On the other hand, some cells may omit a separator membrane ormay include other structures serving a similar purpose. The term“cross-separator pressure differential” is not intended to necessarilyimply that a separator membrane is present in the cell, but merelyrefers to a difference in pressure between the two regions.

With reference to FIG. 1, the electrolyte confinement system may includeat least one enclosed half-cell chamber 132 or 142 with one or morefluid escape elements 160, 162, 164 configured to allow produced gas toescape the half-cell chamber 132, 142. In some cases, a fluid escapeelement 160, 162, 164 may also be configured to allow a quantity ofliquid electrolyte 130, 131 to escape the half-cell chamber 132, 142.The electrolyte confinement system may also include cell structuresconfigured to separate a positive half-cell chamber 132 from a negativehalf-cell chamber 142. Such structures may include a separator membrane106 and a headspace divider 150.

The fluid escape elements 160, 162, 164 may comprise structures thatallow at least gas to escape a half-cell chamber 132, 142. In someembodiments, a fluid escape element may be configured to allow gas onlyor both gas and liquid to escape the half-cell chamber 132, 142 whenfluid pressure exceeds a threshold. In this context, “fluid pressure”may refer to pressure of liquid electrolyte, pressure of a headspacegas, and/or pressure of a “froth” of gas bubbles and liquid electrolytein a dispersed mixture.

In conventional electrolyzer systems, even if gas removal conduits aremaintained at high gas pressures, gases produced at positive and/ornegative electrodes are directed from half-cell chambers to gas removalconduits with few flow restrictions. In most conventional electrolyzers,gas removal conduits also function as out-flow conduits for electrolyte(or process water) which flows through each cell. However, if oneelectrode generates gas bubbles differently than the other electrode(e.g., significantly different bubble sizes, release rates, volumes,etc.), gases may mix with electrolytes at unpredictably different rates.This may lead to an unpredictable (and therefore uncontrollable)transient cross-separator pressure differential, which may in turn causeliquid and/or gas to rapidly cross through the separator from amomentarily higher-pressure half-cell to the momentarily lower-pressurehalf-cell. This “sloshing” effect can lead to unacceptably low gaspurity of a product gas as well as potentially creating an explosive gasmixture.

As used herein, the term “gas separation volume”, “gas separator”,“gas-liquid separator,” or “gas collection volume” may refer to one ormore volumes external to a half-cell 132, 142 into which gas may flow onthe way to being collected in a gas removal manifold 122, 124 whilebeing separated from any liquid (e.g., electrolyte and/or make-upliquid) exiting the half-cell. For example, a gas-liquid separator, suchas gas-liquid separator 184, can include gas collection volume(s) (e.g.,186) and electrolyte capture (collection) volume(s), such as electrolytecollection/capture volume 110. In various embodiments, a gas-liquidseparator may comprise one or more volumes connected in fluidcommunication by one or more fluid pathways and providing separateoutlets for gas and liquid. For example, in some embodiments, a gascollection volume may include an electrolyte capture volume 110, 112 (asdescribed further herein) in addition to a gas removal manifold 122, 124and any conduits or volumes (e.g., 186, 188) therebetween. As usedherein, the terms “gas-liquid separator, “liquid-gas separator,”“gas/liquid separator,” and “liquid/gas separator” are interchangeable.In some embodiments, the terms “gas separator” and “gas-liquidseparator” are interchangeable.

While references in this section are made to FIG. 1, the description isequally applicable to any other embodiments suggested or describedherein. In some embodiments, a fluid escape element 160, 162, 164 mayimpart a resistance to flow in the flow path between a half-cell chamber132, 142 and a corresponding gas-removal manifold 122, 124. Such aresistance to flow may be measurable as a pressure-drop across the fluidescape element 160, 162, 164. For example, in some embodiments, eachhalf-cell chamber 132, 142 may be maintained at fluid pressures higherthan its respective gas-liquid separator by creating a resistance tofluid (gas and/or electrolyte) flowing out of the half-cell chamber 132,142. For example, in some embodiments, this may be accomplished byplacing a flow-restricting fluid escape element 160 in a flow pathbetween a half-cell chamber 132, 142 and a corresponding gas-liquidseparator 182, 184. Limiting a fluid flow rate through a fluid escapeelement 160 may maintain a desired degree of back-pressure or resistanceto fluid flow out of the half-cell chamber 132, 142. Such a flowresistance may beneficially maintain a desired pressure differencebetween an interior of a half-cell chamber 132, 142 and a correspondinggas-liquid separator 182, 184. Such flow-resisting structures mayprevent transient fluctuations in pressures experienced by thegas-liquid separators 186, 184 from being transmitted to the half-cellchambers 132, 142, thereby mitigating fluctuations in pressuredifferences across a separator membrane.

A fluid pressure difference between an interior of a half-cell chamber132, 142 in which a gas is produced and a gas-liquid separator 182, 184arranged to collect the produced gas will be referred to herein as an“exit pressure differential.” In some embodiments, the electrolytecollection volume 110, 112 and the gas-liquid separator 182, 184 arereferred to as an electrolyte capture-and-return system. The electrolytecapture and return system, in some embodiments, may also includeadditional components such as pumps, return channels, valves and thelike. In some embodiments, an electrolyte capture-and-return systemincludes one or more gas-liquid separators, such as gas-liquidseparators 182 and 184, one or more fluid escape elements, such as oneor more egress channels (e.g., 160, 162), and one or more pumps,preferably one or more pumps unique to the respective electrochemicalcell or half-cell, such as pumps 172 and 174, which may be a ventricularpump as described herein with reference to FIG. 3A-3C.

In some embodiments, as in FIG. 1 and FIG. 2 (for example), anelectrolyte capture volume 110 may be a separate volume from a gascollection volume 186, 188. In some embodiments, as shown for example inFIG. 3 (described in further detail below), an electrolyte capturevolume 110, 112 may be the same volume as a volume that includes a gascollection manifold 122, 124.

The exit pressure difference across a fluid escape element (e.g., 160)may be very small (e.g., less than 1 psi; e.g., selected from range of0.1 bar to 1 psi; e.g., 0.5±0.2 bar; e.g., less than or equal to 0.5 barbut greater than 0 bar) as long as the half-cell pressure exceeds thegas-liquid separator (or, gas removal manifold) pressure. In practicalterms, a larger exit pressure differential may allow for greater dampingof variations in a controlled gas-removal manifold pressure. In variousembodiments, the size of an exit pressure difference between an interiorof a half-cell chamber 132, 142 and a gas-liquid separator 182, 184 maybe anywhere from a fraction of one (1) psi to one atmosphere (1 atm orabout 15 psi) or more. In some particular embodiments, the exit pressuredifferential may be as small as about 0.1 bar up to about 1 bar or more.In some particular examples, the exit pressure differential may be atleast 0.01 bar, at least 0.05 bar, at least 0.1 bar, at least 0.2 bar,at least 0.3 bar, at least 0.4 bar, at least 0.5 bar, at least 0.6 bar,at least 0.7 bar, at least, 0.8 bar, at least 0.9 bar at least 1 bar, orup to 2 bar or more. The exit pressure differential may be 0.05 atm to0.35 atm, 0.35 atm to 0.7 atm, 1 atm to 2 atm, or more.

Therefore, in some embodiments, fluid escape elements 160 may beconfigured to limit a flow rate of fluids exiting a half-cell chamber132, 134 and/or to establish a threshold fluid pressure to be exceededbefore fluid will flow through the fluid escape element 160. Fluidescape elements described herein may generally fall into two categories:“series” elements and “parallel” elements.

Series fluid escape elements generally provide a single restrictedpathway for the egress of fluid (i.e., gas, liquid, or mixtures ofboth). In a series element, liquid and gas must follow the same pathwayfrom a high-pressure end to a low-pressure end. As used, herein, seriesfluid escape elements may be broadly referred to as “egress channels.”FIG. 1 and FIG. 2 schematically illustrate example egress channels at160, 260, and 261.

An egress channel (series fluid escape element) may generally comprise along and narrow channel with one end located in a relativelyhigh-pressure region (e.g., a half-cell chamber 132, 142, 232, or 242)and an opposite end located in a relatively low-pressure region (e.g., agas-liquid separator 182, 184, 282, or 284). Egress channels may be“long and narrow” in that they have an interior cross-sectional area (ina plane perpendicular to its flow path) that is small relative to theirtotal path-length. For example, an egress channel may have a total pathlength that is 5 times, 10 times, 100 times, 500 times, 1000 times, (ormore) greater than a cross-sectional dimension (e.g., diameter) of theegress channel. In some cases, an egress channel may also include atortuous path and/or mechanically-restricted conduits. Thus, in variousembodiments, series fluid escape elements (or “egress channels”) maycomprise one-way check valves, “hypodermic” tubes, long and narrowchannels, apertures (e.g., small openings in sheet or plate structures),or other series flow-restricting structures.

In some embodiments, a fluid escape element in the form of an egresschannel may comprise a section of tube of a rigid or flexible materialwith a length several times longer than an internal cross-sectionalarea. Flow limiting channels may be made of materials impervious tofluids flowing through them, such as degradation by hot, alkaline,acidic, and/or other electrolytes that may be used.

Egress channels may beneficially provide a non-linear resistance to flowwhen the fluid is a mixture of liquid and gas. For example, an egresschannel may apply a linear resistance to liquid flow, and adifferently-linear resistance to gas flow, but a randomly dispersedmixture of liquid and gas passing through an egress channel willexperience a non-linear resistance to flow. While not intending to bebound by any particular theory, it is believed the gas and liquidmixture may tend to pass through the egress channel as discrete pocketsof gas and liquid of random volumes. The liquid pockets may tend toexperience a greater resistance to flow due to surface tensioninteractions with the egress channel wall(s), while pockets ofcompressible gas which do not directly experience surface tension withthe walls may tend to be held up by liquid pockets. Compressible gaspockets may also be compressed between liquid pockets in some cases.This non-linear flow resistance may be beneficial in maintaining atleast a desired pressure difference between a half-cell chamber and acorresponding gas-liquid separator.

In various embodiment, different materials, material properties, and/orshapes of an egress channel may affect the degree of liquid flowresistance through the channel. For example, resistance to flow througha channel may be related to surface tension (or hydrophobicity asmeasured by contact angle with the material), wherein a material thatexhibits higher surface-tension with the electrolyte (more hydrophilic,a smaller contact angle) may exert a greater flow resistance than amaterial exhibiting a lower surface tension (more hydrophobic, largercontact angle). Materials which exhibit a contact angle of less than 900are generally referred to as being “hydrophilic” with respect to aparticular fluid, whereas a material exhibiting a contact angle greaterthan 90° is generally referred to as being “hydrophobic” with respect tothat material. In some embodiments, an egress channel material may beselected to be hydrophilic (exhibit a contact angle of less than 90°)relative to the electrolyte. If greater flow resistance is desired, anegress channel material may be selected to be hydrophobic (exhibit acontact angle of greater than 90°) relative to the electrolyte. In someembodiments, an egress channel may comprise a tube of a circularcross-section with an interior tube diameter that is approximately equal(within about 10% difference) to a diameter of a meniscus curve formedby the electrolyte sitting statically in the tube. The same approximaterelationship may hold in the case of non-circular cross-sections (thatis, a side-length of a square or rectangular cross-section channel maybe approximately equal to the meniscus diameter).

In some implementations, an egress channel may be configured to producea non-linear flow resistance that is “self-correcting” in that, a largevolume of gas escaping through the egress channel will tend to cause arise in liquid level within the half-cell chamber (e.g., as liquid isdriven into the half-cell chamber by a pump and/or as make-up liquidenters the half-cell as further described below). When the liquid levelrises to the level of the egress channel entrance, a volume of liquidmay enter the egress channel which will tend to momentarily increase theflow resistance through the channel and correspondingly increasingpressure in the half-cell chamber as gas continues to be produced at thesame rate as before the rise in flow resistance. These changes inpressure and liquid level occurring in each half-cell within a stack maybe very small and may occur very quickly (within a second or less),meaning this self-correction may automatically correct for pressurechanges too small to be corrected for with pressure regulators acting tocontrol pressures in the gas-removal manifolds at the stack-level.

This same behavior may also be described as a passive closed-loopcontrol system for minimizing pressure differences across the separatormembrane by automatically reversing transient pressure changes. In thisway, the electrolyte acts as a mechanical transducer, convertingelectrolyte liquid level to a differential pressure through the egresschannel. Electrolyte level acts as a pressure sensor as decreasing fluidpressure in the half-cell corresponds to an increased liquid level. Theelectrolyte entering the egress channel (once electrolyte rises to thelevel of the egress channel inlet) increases the flow resistance throughthe egress channel, and thereby increases the pressure in the half-cellto return the half-cell chamber to a higher pressure. By providing suchfeatures and functions in both half-cell chambers, transient pressurechanges in both half-cells may be rapidly returned to an equilibriumstate, thereby balancing pressure differentials between the half-cells.

Therefore, in other embodiments, any other mechanism (includingdigitally-controlled electromechanical devices or otherpassively-operated control devices) may be used to increase a resistanceto gas (and/or liquid) flow exiting a half-cell chamber in response to adecrease in that half-cell's pressure or a rise in electrolyte-level inthe half-cell. In some embodiments, such control systems may beconfigured to achieve the desired pressure-balancing while substantiallypreventing electrolyte from escaping the half-cell. For example, in oneembodiment, a floating valve may be configured to increase pressure drop(flow resistance) through a fluid escape element (e.g., a channel,membrane, or aperture) when a liquid level in the half-cell rises,and/or to decrease pressure drop (flow resistance) through the fluidescape element when a liquid level in the half-cell falls. In otherembodiments, an electromechanically controlled valve (such as a solenoidvalve) may be driven by an electronic controller programmed to increaseflow resistance in response to one or more electrical or mechanicalsensor signals indicating a drop in fluid pressure within a half-cellchamber. In some such embodiments, this pressure-balancing function maybe achieved while omitting pumps associated with each half-cell.

In some embodiments, egress channels configured to serve as fluid escapeelements may be formed integrally within other structures in a cell,such as a half-cell chamber wall (e.g., a cell-frame plate), a bipolarplate, cell structural elements, or other features. In some embodiments,egress channels may be formed in cell structures (e.g., cell-frames,cover sheets, or other cell-frame structures) by machining,laser-cutting, lithographic techniques, additive manufacturingtechniques (e.g., 3D printing), or other methods. In other embodiments,egress channels may be formed by securing (e.g., embedding, attaching,over-molding, or otherwise) a separate structure (such as a tube, valve,channel, or others) made of a different material into a cell-framestructure. Egress channels may comprise straight linear paths, curvedpaths, or combinations of straight and curved paths.

In other embodiments, an egress channel may comprise a section of tubingbent or otherwise formed into a desired shape and embedded in orattached to a cell-structure such as a cell-frame plate, a bipolarplate, cell structural elements, or other features. For example, such atube may be a circular cross-section tube made of a material imperviousto electrolyte and exhibiting a desired degree of hydrophobicity orhydrophilicity with the electrolyte. In some particular examples, such atube may be a metal or a metal alloy comprising metals such as nickel,titanium, aluminum, or others. Alternatively, such a tube may compriseor be made of one or more polymer materials such as polyamide (PA),poly(tetrafluoroethylene) (PTFE), polyvinylidine fluoride (PVDF),poly(vinyl chloride) (PVC), polysulfone (PSU), polyphenylsulfone (PPSU),polyetheretherketone (PEEK), FEP (fluorinated ethylene propylene), PFA(perfluoroalkoxy), ETFE (ethylene tetrafluoroethylene), or others. Tubesmay be embedded in a cell-frame by over-molding, adhesives, solvents,welding, or other techniques.

For example, in some embodiments, an egress channel may have a spiral orhelical section, such as a coiled tube. In other embodiments, an egresschannel may have both curved segments and straight segments, straightsegments and sharp-angled turns (e.g., bends of any acute or obtuseangle), or only straight segments. Egress channels may also be orientedin any configuration relative to gravity. In other words, egresschannels may be oriented such that fluid flows upwards, downwards,horizontally, or various combinations of directions while traveling frominside a half-cell chamber to a point outside the half-cell chamber. Insome embodiments, a filter may be positioned at an inlet end of anegress channel. Such a filter may comprise a porous metal (e.g., a metalmesh or foam), polymer, or other material suitable for allowing liquidand gas to pass through while trapping solid particles in the porousfilter.

In some embodiments, fluid escape elements may comprise one or moreone-way check valves, such as duckbill valves, poppet valves, ball checkvalves, diaphragm check valves, tilting disc check valves, flappervalves, lift check valves, umbrella check valves, piston check valves,swing check valves, dual plate (double-door) check valves, or others.One-way check valves may be made of any suitable material such aspolymers, metals, ceramics, or other material or material combinationsselected to be resistant to damage from the liquid electrolytes andgases contacting the valve. Check valves may be configured with acracking pressure—that is a threshold pressure difference between adownstream-side of the valve and an upstream side that must be exceededbefore fluid will flow through the valve. In some embodiments, thecracking pressure of a check valve may be selected to maintain a desiredexit pressure differential between a half-cell chamber and a gas-liquidseparator.

FIG. 1 also shows an egress channel fluid escape element 160 between thenegative half-cell chamber 142 and its corresponding electrolyte capturevolume 110. The egress channel element 160 is shown allowing a smallquantity of liquid 190 to pass through the channel and drip into theelectrolyte capture volume 110.

In some embodiments, fluid escape elements may be arranged symmetricallysuch that each half-cell has the same number and/or flow rate capacityof fluid escape elements as its counter-half-cell. In other embodiments,cells may be configured with asymmetrical fluid escape elements, suchthat one half-cell has a greater fluid escape flow capacity than itscounter-half-cell.

FIG. 2 schematically illustrates another embodiment of one cell 200configured to confine electrolyte to the cell 200. Each half cellchamber 232, 242 is shown separated from respective gas-liquidseparators 282, 284, joined only by an egress channel 260, 261 providingthe sole fluid-communication channel out of the half-cell chamber 232,242 into the gas-liquid separator 282, 284.

The egress channel 260, 261 providing the only pathway for fluid to flowfrom the half-cell chamber into the gas-liquid separator may allow theegress channel height to establish a height of a liquid level within thehalf-cell chamber 242, 232, thereby defining a height and volume of theheadspace 244, 234 in each half-cell chamber 242, 232. Therefore, thevertical position of an egress channel opening 262, 263 within ahalf-cell chamber 242, 232 may be positioned at a height within thehalf-cell chamber 242, 232 selected as a desired approximate maximumheight of an electrolyte liquid level within the half-cell chamber 242,232. When an electrolyte liquid level rises above the opening of theegress channel 262, 263, the fluid flowing through the egress channel260, 261 will tend to be entirely or predominantly liquid electrolyte.When the liquid electrolyte level drops below the height of the egresschannel opening 262, 263, the fluid flowing through the egress channel260, 261 will tend to be entirely or predominantly gas. Establishing aminimum headspace by establishing an approximate maximum liquidelectrolyte level may advantageously leave the headspace clear foraddition of a consumable make-up liquid and may help prevent electrolytefrom flowing backwards up through the make-up liquid inlet 276, amongother advantages.

In some embodiments, an egress channel outlet 264, 265 may be configuredto drip electrolyte into the electrolyte capture volume 210, 212 whileallowing gas to flow to a gas removal manifold 222, 224.

In various embodiments, a fluid escape element configuration in apositive half-cell may be the same as the fluid escape elementconfiguration in a corresponding negative half-cell, or fluid escapeelement configurations may be different in opposite half-cells of acommon cell. Similarly, adjacent cells may have the same or differentconfigurations relative to one another with respect to fluid escapeelements or other features.

For example, egress channel inlets 263 and outlets 265 in a positivehalf-cell chamber 232 and a positive gas-liquid separator 284 may bepositioned at substantially the same height as egress channel inlets 262and outlets 264 in a negative half-cell chamber 242 and a negativegas-liquid separator 282 of the same cell 200. Alternatively, egresschannel inlets 263 and outlets 265 in a positive half-cell chamber 232and a positive gas-liquid separator 284 may be positioned at a higher orlower height compared with a negative half-cell chamber 242 and anegative gas-liquid separator 282 of the same cell 200.

Parallel fluid escape elements may include porous structures such asmembranes, filters, meshes, porous blocks, or other structures having aplurality of tortuous or small-diameter pathways from one side throughto another side. Which of the parallel paths any particular quantity ofa fluid may pass through may tend to be influenced by the physicalstructure of porous structure, the structure of other cell components,and/or the physics of actions occurring in the cell. Due to thedifferences in physical interactions of liquids and gases with a porousfluid escape element, liquids may pass through some pores more slowly(e.g., due to friction, surface tension, viscosity, etc.) while somepathways may become at least temporarily blocked by (or filled with)liquid, causing gases to pass through un-blocked pores or pathways.

Some fluid escape elements may also be configured to be “phasediscriminatory” such that only one phase of matter (e.g., liquid or gasbut not both) is permitted to pass through. In some embodiments, atleast some degree of phase discrimination may be achieved with highlyhydrophobic materials. In some examples, such hydrophobic materials mayinclude porous membranes that may allow transmission of gaseous matterwhile preventing transmission of liquids. FIG. 1 illustrates examplemembrane fluid escape elements at 162 and 164. In some embodiments,membranes that are not necessarily phase discriminatory may be used asfluid escape elements.

Membranes with sufficiently small and/or tortuous hydrophobic pores mayprevent transmission of liquid droplets or mist in addition topreventing transmission of bulk liquid flow. For example, suitablemembranes may have pore sizes as small as 0.1 m or smaller. Suitablefluid escape element membranes may be made from various materialsincluding polytetrafluoroethylene (PTFE), expanded PTFE (ePTFE),polyethersulfones (PES), FEP (fluorinated ethylene propylene), PFA(perfluoroalkoxy), ETFE (ethylene tetrafluoroethylene), polypropylene,polyethylene, polycarbonates, polyvinylidenefluoride, celluloseacetates, polyacrylonitrile, polyetherimides, polyamide, cross-linkedpolyether, polypropylene, or various combinations of these and otherpolymers. In other examples, a parallel fluid escape element maycomprise a block, sheet, or plate of a porous composite or ceramicmaterial. Such materials may be naturally hydrophobic or may be modifiedby treatments or additives to impart hydrophobic properties. In otherembodiments, a hydrophobic material may be combined with a hydrophilicmaterial to form a composite membrane structure for use as a parallelfluid escape element.

In some embodiments, two or more fluid escape element structures may becombined. For example, one or more one-way valves or apertures may becombined with an egress channel in order to create a fluid escapeelement with two or more series fluid escape elements in series with oneanother. In another example, one or more series fluid escape elements(e.g., an egress channel, valve, aperture, etc.) may be combined withone or more parallel fluid escape elements (e.g., a membrane or porousblock).

In various embodiments, one, two, three, or more fluid escape elementsof the same or different types may be positioned in a fluid path betweena half-cell chamber and a gas-liquid separator. For example, FIG. 1illustrates three fluid escape elements separating each half-cellchamber from its respective gas removal manifold 122, 124. A firstmembrane-type fluid escape element 164 is shown positioned between anegative half-cell chamber 132, 142 and an electrolyte capture volume110, 112 (described in further detail below) and a second membrane-typefluid escape element 164 separating the electrolyte capture volume 110,112 from a gas removal manifold 122, 124. In various embodiments, one orboth membranes 162, 164 may be phase-discriminating hydrophobicmembranes made of a material and construction capable of allowing onlygas to pass through, causing liquid or mist to collect and drip backinto the higher-pressure chamber. In some embodiments, one or bothmembranes 162, 164 may be non-phase discriminatory.

In various embodiments, a cell 200 may include a headspace divider 250configured to divide a gas headspace 234 of one half-cell 232 from thehas headspace 244 of its counter-half-cell 242. Such a headspace divider250 may be made of any suitable material and construction such that ithas the properties of being impermeable to degradation by gases producedin either half-cell and impermeable to degradation by the liquidelectrolyte. Suitable examples may include a solid non-porous sheet ofan electrolyte-impervious polymer, metal, metal oxide, metal hydroxide,ceramic, or composite material. In some embodiments, a headspace divider250 may be made of a flexible material that is impervious to theelectrolyte and to gases in the half-cell chambers. Such a flexibleheadspace divider may deflect due to differences in fluid pressure atthe divider interface, thereby allowing a degree of passively-automaticpressure-balancing between the half-cell chambers. Below the headspace234, 244, the half-cell chambers 232, 242 may be divided by a separator206.

In various embodiments, a separator (106 in FIG. 1, 206 in FIG. 2, orany other separator in an electrochemical system described herein) maybe made of one or more of various materials, including nylon,polyethylene (PE), polypropylene (PP), polyolefins (PO), polyamide (PA),poly(tetrafluoroethylene) (PTFE), polyvinylidine fluoride (PVdF),poly(vinyl chloride) (PVC), polysulfone (PSU), polyphenylsulfone (PPSU),polyetheretherketone (PEEK), asbestos, zirconium oxide cloth, cotton,polyvinyl alcohol or polyvinyl acetate (PVA), ethyl-cellulose,methyl-cellulose, ethylene-methacrylic acid copolymers, fluorinatedpolymers, sulfonated polymers, carboxylic polymers, woven or non-wovencellulose, NAFION, or others. In some embodiments, a separator materialmay be modified by addition of cross-linking agents or bypost-treatments such as corona discharge treatments for modifyingsurface features of the material such as modifying a hydrophilicity orhydrophobicity of the material. A degree of hydrophilicity and/orhydrophobicity of a membrane material may also be modified by inclusionof one or more additive materials tending to affect such parameters. Forexample, hydrophilic additives such as zirconia, titania, or othermaterials may be embedded in or co-extruded with a polymer membrane. Insome embodiments, ceramic membranes, cermet membranes, or compositeceramic/polymer membranes may also be used. Example ceramic and cermetseparator membranes are described in U.S. Pat. Nos. 4,898,699,4,445,994, and US20150118592.

In some embodiments, a separator may be made of a suitable material andconstruction so as to be substantially hydrophilic and/or impervious toone or more gases. In some embodiments, separators may be made ofmaterials from the class of materials known as ionomers, including anionexchange membranes and proton exchange membranes, which are typicallysolid non-porous materials capable of conducting ions without allowingdiffusion or direct flow of liquids or dissolved species. Examples ofionomers include ethylene-methacrylic acid copolymers such as thatproduced by DUPONT® under the trademarks SURLYN® and NUCREL®,fluoropolymer-copolymers such as that produced by DUPONT® under thetrademark NAFION®, or others.

In some embodiments, separators may include solid-gel materials orcomposite materials such as the separator materials described in USPatent Application Publications US20020012848, US20020010261,US20030099872, and US20120148899, U.S. Pat. Nos. 3,953,241, 6,358,651,and 6,183,914, or European Patent EP0624283B1. For example, a compositematerial separator membrane may comprise a polymer membrane (e.g., madeof one or more of the materials described above) impregnated with ametal oxide or metal hydroxide (e.g., oxides, dioxides, sub-oxides, orhydroxides of metals such as zirconium, aluminum, lithium, titanium,magnesium, etc.).

In various embodiments, the electrodes 102, 104, 202, 204 may compriseany structure, materials, and catalysts suitable for enabling desiredreactions in the electrochemical cell. Electrodes typically comprise aconductive substrate (e.g., a sheet, felt, foam, mesh, or otherstructure of metal, carbon, graphite, conductive polymer or otherelectrically conductive material) and a catalyst supported eitherdirectly on the conductive substrate or on a separate layer contactingor attached to the conductive substrate. Some electrodes may alsocomprise a gas diffusion layer containing a hydrophobic polymer. Someexample electrode structures, catalysts and materials are provided inthe Jensen Report referenced above. Other example electrode structuresare described in U.S. Pat. No. 9,938,627, US Patent ApplicationPublication 2015/0292094, and U.S. Pat. No. 10,026,967, each of which isherein incorporated in their entirety by reference.

In various embodiments, a cell-stack made up of confined electrolytecells may be initially filled with electrolyte in any of a variety ofways. For example, a portion of a cell-volume may be filled with a drypowder that may be hydrated and dissolved by make-up liquid deliveredvia a make-up liquid supply manifold. In other embodiments, electrolytemay be added as a solid frozen block of electrolyte included duringassembly of a cell-stack. In still other embodiments, electrolyte may bedelivered into each cell volume in a cell-stack via a make-up supplymanifold, a gas-purge manifold, or a specially-provisionedelectrolyte-fill manifold.

Electrolyte Capture and Return System

FIG. 1 and FIG. 2 illustrate example features and structures referred toherein as part of an electrolyte capture and return system in which eachhalf-cell chamber 132, 142, 232, 242 may be joined to an electrolytecapture volume 110, 112, 210, 212 arranged and configured to receive andretain a volume of electrolyte 130, 131 that escapes the half-cellchamber 132, 142, 232, 242, to separate the captured liquid electrolytefrom gas leaving the half-cell chamber, and to return the capturedelectrolyte to one or both of the half-cell chambers. The electrolytecapture volume 110, 112, 210, 212 may comprise an outlet conduit 118,119 joined to a return path conduit 114, 116 and a pump 172, 174 forreturning electrolyte 130, 131 to the cell 100 from which it escaped.

In some embodiments, the electrolyte capture volume 110, 112, 210, 212may be joined in fluid communication with a gas collection volume 186,188, 286, 288 which may be in fluid communication with a gas removalmanifold 122, 124, 222, 224. Together, an electrolyte capture volume anda gas removal volume may be configured to substantially separate a fluidmixture exiting a half-cell chamber 134, 132, 242, 232 into gas in thegas collection volume 186, 188, 286, 288 and liquid electrolyte in theelectrolyte capture volume 110, 112, 210, 212.

In some embodiments, as shown for example in FIG. 1, an electrolytecapture and return system may be configured to return capturedelectrolyte 130 or 131 exclusively to the half-cell chamber 132, 142from which it was captured without allowing mixing with electrolyte 131or 130 captured from a counter-electrode half-cell chamber 132, 142.

In some embodiments, as shown for example in FIG. 2, an electrolytecapture and return system may be configured to allow electrolytecaptured from opposite half-cell chambers 232, 242 of a common cell 200to mix in a common volume such as an expansion volume (described infurther detail below).

In various embodiments a capture volume may be configured with a widerange of suitable structures and materials. For example, in someembodiments, a capture volume for each half-cell chamber 132, 142, 232,242 may be integrated into one or more cell-frame or structures in abipolar or monopolar stack configuration. In other embodiments, capturevolumes and conduits may be provided external to a cell-frame andconfigured to direct captured electrolyte back into the cell.

In some embodiments, a capture volume 110, 112, 210, 212 may be an emptyvolume containing only gas and/or liquid electrolyte. In otherembodiments, a capture volume 110, 112, 210, 212 may contain one or morecondensation materials suitable for condensing liquid electrolytedroplets from a fluid mixture escaping an associated half-cell.Condensation materials may generally feature high surface area materialsimpervious to degradation by electrolyte. Such condensation materialsmay include porous structures of metal and/or non-metal materials, suchas woven or non-woven polymer or metal mesh, sheet, foam, grids, orexpanded materials with three-dimensional structures. In other examples,condensation materials may comprise particles of one or more materials(e.g., ceramics, metals, or metal oxides) either loose, polymer-bound,or as sintered structures. The capture volume 110, 112, 210, 212 of theliquid-gas separator 182, 184, 282, 284 may comprise a gas pocket regionabove a liquid level in a liquid region.

In general, a volumetric capacity of a capture volume may be sized so asto provide a sufficient volume for capturing enough electrolyte toaccommodate a maximum electrolyte egress rate from a half-cell chamber.As described elsewhere herein, the liquid content of fluid escaping ahalf-cell chamber at any given time may depend on a stage of operationof the cell at that time. In some embodiments, the ideal size of anelectrolyte capture volume may also depend on a rate at which capturedelectrolyte is returned to the cell from which it escaped. The rate atwhich electrolyte is returned may be a function of a pumping rate.

In some embodiments, a capture volume may be constructed to have avariable volume, such as by the use of a movable piston or an expandablediaphragm, an expandable membrane, or a resilient expandable tube orconduit that may be displaced or expanded as more electrolyte isintroduced to the capture volume 110, 112, 210, 212.

In some embodiments, it may be desirable to exclude gas from a bottomportion 220 of a capture volume 110, 112, 210, 212 so as to ensure thatonly liquid electrolyte is drawn into a pump 172, 174, 272, 274 andreturned to a half-cell chamber 132, 142, 232, 242. For example, in someembodiments a section of a porous hydrophilic material 126, 226 may bepositioned near a bottom portion of a capture volume 110, 112, 210, 212so as to substantially limit formation of gas pockets adjacent to acapture volume outlet 118, 119, 218, 219. A porous hydrophilic materialor membrane 126, 226 with a bubble point greater than an intake pressureof a pump 172, 174 may be used. Bubble point is the gas pressure atwhich gas bubbles pass through a membrane, and is a metric often listedin catalogs for membranes used in industries such as water filtration.The bubble point of a membrane or material may also be determinedempirically.

Example materials or membranes 126, 226 may include polysulfonemembranes, polyethersulfone membranes, sulfonated polyethersulfonemembranes, polyacrylonitrile membranes, polyvinylidene difluoridemembranes, membranes made from mixed cellulose esters, celluloseacetate, nylon, polyester, porous ceramic structures, three-dimensionalporous metal structures such as meshes, grids, or foams (e.g., nickel,titanium, or other metals or metal alloys), ceramics, cermets,composites, or combinations of these or other materials.

A similar objective may be achieved with a floating divider configuredto float on top of any electrolyte 130, 131 within the capture volume110, 112, 210, 212. In some embodiments, a floating divider may beconfigured to seal the capture volume outlet 118, 119, 218, 219 so as toprevent gas from exiting the capture volume outlet when the capturevolume contains no liquid electrolyte, or contains less than a thresholdvolume of liquid electrolyte. In still other embodiments, otherphase-separating materials or structures may be used to allowsubstantially only liquid electrolyte to occupy a bottom region 220 ofan electrolyte capture volume 110, 112, 210, 212 adjacent to an outlet118, 119, 218, 219.

In other embodiments, hydrophilic membranes, floaters or otherstructures may be omitted so as to allow gas to exit the capture volume110, 112, 210, 212 through the outlet 118, 119, 218, 219. Any gasexiting the capture volume 110, 112, 210, 212 via the outlet 118, 119,218, 219 may be pumped into one or both half-cell chambers 132, 142,232, 242.

Some embodiments of a capture volume 110, 112, 210, 212 may comprise anoutlet 118, 119, 218, 219 with a one-way valve 221 to prevent back-flowof electrolyte from a return conduit 114, 116, 214, 216 back into theelectrolyte capture volume 110, 112, 210, 212. Any type of one-way valve(or check valve) may be used, such as duckbill valves, poppet valves,ball check valves, diaphragm check valves, tilting disc check valves,flapper valves, lift check valves, umbrella check valves, piston checkvalves, swing check valves, dual plate (double-door) check valves, orothers. One-way check valves may be made of any suitable material suchas polymers, metals, ceramics, or other material or materialcombinations selected to be resistant to damage from the liquidelectrolytes and gases contacting the valve. In some embodiments, aone-way valve may be integrated into a pump arranged to move fluid fromthe electrolyte capture volume 110, 112, 210, 212 through a returnconduit 114, 116, 214, 216 into a half-cell chamber 132, 142, 232, 242.

In some embodiments, an electrolyte capture and return system and/or amake-up liquid supply system may operate without a liquid level sensor.In some conventional electrochemical cells, a liquid level sensor istypically used to control a rate of make-up fluid addition, a rate ofelectrolyte flow through the cell, and/or a rate of gas extraction froma cell. Instead, the described systems and methods utilize pressuredifferentials, fluid escape elements, and check valves to precisely, butpassively, manage electrolyte levels and make-up fluid addition rateswithout the need for electronic controllers, sensors, liquid levelsensors, etc. This may be advantageous in that it decreases cost andeliminates failure modes and error associated with sensors,electromechanical actuators, and electronic control systems, therebydecreasing the need for maintenance, down-time, and replacement.

A pump 172, 174, 272, 274 may be arranged along an electrolyte returnconduit for transporting fluid (e.g., electrolyte, gas, and/or otherfluid) from an electrolyte capture volume 110, 112, 210, 212 to ahalf-cell chamber 132, 142, 232, 242. In embodiments, the pump 172, 174,272, 274 may comprise one or more positive displacement pump types, suchas a piston pump, a peristaltic pump, a rotary lobe pump, a progressingcavity pump, a screw pump, a rotary gear pump, a diaphragm pump, a gearpump, a vane pump, or other positive displacement pumps or other pumptypes. In various embodiments, any number of pumps may be used forreturning captured electrolyte to cells for a stack. In someembodiments, a system may use one pump per cell, one pump per half-cell,one pump for an entire stack of cells, or one pump for all positivehalf-cells of a stack and a second pump for all negative half-cells fora stack. Other configurations are also possible.

In some embodiments, a pump 172, 174, 272, 274 may be configured andarranged to return electrolytes to a cell or half-cell chamber in a“pressure balanced” manner, that is, without increasing fluid pressurein the half-cell chamber 132, 142, 232, 242 above a predeterminedthreshold. In some embodiments, this may be accomplished by activecontrols using sensors and a closed-loop control system, while in someembodiments, “pressure balancing” of a pump/cell system may beaccomplished passively by using a pressure balancing pump type.

One type of “pressure balancing” pump that is well-suited to use withthe various systems and methods described herein is referred to hereinas a “ventricular pump,” an example of which is illustrated in FIG. 3.

Pressure-Balancing “Ventricular” Pump

FIG. 3A schematically illustrates an example “ventricular pump” 300 thatmay be used in various aspects of electrochemical system embodiments asdescribed herein. The ventricular pump advantageously allows for passivepressure regulation of pumped fluids and may also simultaneously drivefluid flow in a large number of parallel or simultaneous flow channelswith a single simple actuation mechanism. Ventricular pumps may alsocomprise a minimum of moving parts, may be made of inexpensive materialsthat are highly compatible with caustic fluids to be pumped, and may beintegrated into bipolar or monopolar cell-stacks.

Ventricular pumps operate by applying a pressure to an actuation fluid(i.e., a compressible or incompressible fluid) in contact with one ormore compressible “driver” elements. The applied pressure issimultaneously transmitted to the compressible driver elements (e.g.,compressible tubes, diaphragms, or other deflectable structures),thereby driving fluid out of or away from the compressible elements. Thedirection of flow through a ventricular pump may be passively controlledby one-way check valves.

FIG. 3A is a schematic illustration in which a ventricular pump 300 maycomprise a housing 310 with a plurality of fluid-driving tubes 312extending through an interior of the housing 310 which is filled with anactuation fluid 320 surrounding the tubes 312. Each tube 312 may becoupled to an upstream fluid conduit 324 outside of a first end wall 332and a downstream fluid conduit 326 outside of a second end wall 334 ofthe housing 310. An upstream one-way valve 342 and a down-stream one-wayvalve 344 may be placed in each tube 312 or conduit 324, 326. Both theupstream valve 342 and the down-stream valve 344 may be arranged toallow fluid flow in a first direction through the tube (e.g., downwardsin the orientation illustrated in FIG. 3A) and to prevent fluid flow inthe opposite direction. The ventricular pump 300 may also include anactuator 350 arranged to apply a fluid pressure to the actuation fluid320 contained within the housing 310 and surrounding the tubes 312.

As used herein, the term “driver element,” “fluid driver” or simply“driver” refers to a structural ventricular pump component thatcomprises a compressible or deflectable structure which, when compressedor deflected by an actuation fluid, drives a transported fluid through afluid-carrying conduit. In the schematic example of FIG. 3A, the tubes312 comprise both a deflectable structure (the compressible tube walls)and a fluid-carrying conduit (the lumen volume within the tube).Therefore, the tubes 312 of FIG. 3A may be described both as a “driver”and as a portion of a conduit through which fluid is driven by actuation(compression or deflection) of the driver. The term “driver” is intendedto be equivalent to other terms such as “compressible element,”“deflectable element,” “compressible conduit section” or other termssuggesting similar structures.

In some embodiments, fluid drivers represented as tubes 312 in FIG. 3Amay be made of incompressible materials such as hard plastics, metals,ceramics, etc., but arranged in a configuration allowing for compressionof a chamber, such as pistons, bellows, diaphragms, etc. Fluid driversmay include any structure of any shape or arrangement capable oftransmitting a (positive or negative) pressure applied by the actuator350 to a fluid-carrying conduit 312 in order to drive fluid within theconduit 312 from an upstream end 352 to a downstream end 354.

A ventricular pump 300 may operate to convey fluid from an upstream end352 toward a downstream end 354 of each flow channel defined by a tube312 and corresponding upstream conduit 324 and downstream conduit 326when an actuator 350 compresses the actuation fluid 320. The increasedpressure applied to the actuation fluid 320 will be transmitted to thesections of each compressible element 312 within the fluid, therebyexpelling a volume of fluid through the down-stream one-way check valve344. The fluid in the tubes 312 will be prevented from flowing backwardsby an upstream one-way valve 342. Upon release of the compressivepressure on actuation fluid 320 and the tube 312, if a fluid pressureupstream of an upstream valve 342 is greater than the reduced pressurewithin the housing 310 (and therefore within the tubes 312), fluid mayflow in a downstream direction through the upstream valve 342 into thecorresponding inner tubing section 312. In some embodiments, a negativepressure may be applied to the actuation fluid in order to draw upstreamfluid into the tubing sections 312.

In some embodiments, the compressible elements 312 (or one-way valves,diaphragms, or other flexible structures described herein) may be madeof any of one or more resilient compressible materials with rubber-likeproperties, such as, latex rubber, vulcanized rubber, silicone, naturalrubber, isoprene, isobutylene isoprene, epichlorohydrin,polychloroplene, pefluoroelastomers styrene butadiene rubber (SBR),other butyl rubbers, ethylene propylene diene terpolymer (EPDM), otherethylene propylene rubbers, nitrile, neoprene (polychloroprene orpc-rubber), chlorosulfonated polyethylene (CSPE or HYPALON),fluoroelastomers, or others.

While FIG. 3A illustrates circular cross-section tubing, the tubing orother compressible elements may be any cross-sectional shape as desired.In some embodiments, compressible elements may be made of a materialthat is itself substantially incompressible, but in a cross-sectional orother shape that is capable of being compressed or deflected to reducean interior volume containing a fluid to be pumped. In otherembodiments, tubing, compressible elements, or other fluid driverelements may be made of a compressible material.

While resilient compressible fluid driver materials may be beneficial inthat they may be actuated by either positive or negative actuationpressures and may be self-expanding on the release of actuationpressure, the fluid drivers need only be capable of being compressed ordeflected by the actuation fluid 320. Resilience is not a necessaryproperty of the tubing. Therefore, other non-resilient orminimally-resilient compressible materials may be used, such aspolytetrafluoroethylene tubing, polyvinyl tubing, or others.

The number of independent flows (i.e., combinations of inflow andoutflow conduits 324, 326 and conduits 312) controllable by aventricular pump 300 is limited only by the number of fluid drivers andconduits 312 that may fit within a housing 310. Therefore, a ventricularpump 300 may be configured to hold any number of parallel pumping flowsby choosing a housing size and conduit or fluid driver sizes.

In various embodiments, the housing 310 should be sealed against leakageof the actuation fluid 320. Therefore, any conduit tubes 312, orconduits 324, 326 attaching to or extending through the housing 310 maybe sealed to the housing 310. In some embodiments, the tubes 312 and/orconduits 324, 326 may be sealed to the end plates such as by welds,adhesives, fittings, couplings, or other mechanisms or methods. Forexample, in some embodiments, the housing end caps 332, 334 may havestraight, threaded, or barbed connectors attached to or integrallyformed with the end caps. For example, connectors may be molded as partof the end caps (or other housing part), machined, 3D printed, etc.

In various embodiments, the fluid drivers 312 within the housing 310 maybe a different material than fluid-carrying conduits 332, 334 locatedoutside of the housing 310. Therefore, in some examples, an upstreamfluid-carrying conduit 324 may be made of a first material and may bejoined to an outer coupling which may be attached to or integrallyformed with a housing section. A corresponding fluid driver section 312may be joined to an inner coupling which may be attached to orintegrally formed with an interior housing section. In some embodiments,an upstream 324 and/or downstream fluid-carrying conduit 326 may beintegrally formed with a portion of the housing 310 or one or more partsattached to the housing 310, such as an end-cap or a side-wall.

While FIG. 3A illustrates fluid conduits 324, 326 and fluid driverconduits (tubes) 312 extending in a straight line through opposite ends332, 334 of the housing 310, this need not be the case in allembodiments. In some embodiments, an inflow (upstream) conduit 324 and acorresponding outflow (downstream) conduit 326 may pass through the samehousing wall as one another (e.g., an end-wall, end-cap, or side-wall).In some embodiments, an upstream inflow conduit 324 and a correspondingdownstream outflow conduit 326 may pass through housing wallsperpendicular to one another, or at any other orientation relative toone another. In such embodiments, compressible fluid driver conduits(e.g., tubes) 312 or other conduit structures within the housing maycurve or bend within the housing 310.

In some embodiments, only a portion of a fluid driver 312 within thehousing 310 may be compressible while other portions of a fluid-carryingconduit may be made of an incompressible material that merely directsfluid flow. In some embodiments, a ventricular pump may be configuredwith two or more upstream inflow conduits 324 or downstream outflowconduits 326 joined to one another in a manifold or other configurationallowing for two or more flow streams to be joined on an inlet and/oroutlet end.

While the housing 310 in FIG. 3A is shown as having a cylindrical shapeindependent of other structures, in various embodiments the housing 310may be any other shape as desired, such as spherical or a prismaticshape such as a rectangular or other prism. In various embodiments, thehousing may be made of any materials or combinations of materialsincluding plastics, metals, ceramics, or composite materials suitablefor the actuation fluid and actuation pressures desired.

In some embodiments, a housing 310 may be integrated into anelectrochemical cell-stack such as by forming a housing volume byjoining multiple stacked layers. For example, a housing 310 may comprisea manifold, conduit, or other structure joining portions of multiplecell-stack layers into a common volume which may contain an actuationfluid and fluid drivers 312 for each of a plurality of individual cellsor half-cells. An example is described below with reference to FIG.3B-FIG. 3C.

In various embodiments, the one-way valves 342, 344 in a ventricularpump 300 may include any one-way check valve type such as duckbillvalves, poppet valves, ball check valves, diaphragm check valves,tilting disc check valves, flapper valves, lift check valves, umbrellacheck valves, piston check valves, swing check valves, dual plate(double-door) check valves, or others. One-way check valves may be madeof any suitable material such as polymers, metals, ceramics, or othermaterial or material combinations selected to be resistant to damagefrom the liquid electrolytes and gases contacting the valve. Althoughone-way valves 342, 344 are shown positioned outside of the housing 310,they may alternatively be positioned inside the housing volume or withincouplings, end-caps, or other structures of the housing itself. WhileFIG. 3A illustrates only one upstream valve 342 and one downstream valve344 per conduit, a ventricular pump 300 may include any number of valvesin a single tube or conduit.

FIG. 3A illustrates an actuator 350 in the form of a simple piston 356which may apply a positive pressure as the piston 356 moves towards thehousing 310, and in some embodiments may apply a negative pressure bymoving the piston 356 away from the housing 310. In variousimplementations, any type of actuator may be used in place of or incombination with a piston. For example, in some embodiments, an actuator350 may comprise a piston pump in which a piston is driven by a rotaryor linear motor. In other embodiments, an actuator 350 may comprise anyother pump type capable of intermittently applying an increased pressureto a fluid. Some examples of such pumps may include syringe pumps,peristaltic pumps, or other type of intermittently-actuated positivedisplacement pump. In other embodiments, an actuator 350 may comprise anelectronically-controlled solenoid, servo, or other electromechanicaldevice. In other embodiments, an actuator 350 may comprise a pressureregulator actuatable to intermittently apply a pressure from ahigh-pressure (or low-pressure) source, such as a compressed-gas sourceor a pressurized liquid source, to the actuation fluid.

In various embodiments, the frequency of actuation (i.e., how often anactuation pressure is applied per unit of time) may be chosen based on adesired rate of pumping (e.g., in terms of fluid volume or mass per unittime), which may be chosen based on a volume of fluid to be moved by theventricular pump. A magnitude of pressure applied by an actuator mayalso be selected based on other system parameters, such as an expectedor desired down-stream pressure.

However, the actuation pressure need not be tightly controlled, becausethe volume of fluid driven out of each fluid driver 312 during eachactuation may simply be the compressible interior volume of the tube orother compressible or deflectable driver section. Over-compression ofthe fluid drivers 312 may be tolerated by selecting compressiblematerials capable of withstanding the excess pressure. On the otherhand, a maximum actuation pressure may be selected based on a desiredmaximum downstream pressure. If a pressure in a particular conduit 326downstream of a downstream valve 344 exceeds (or is equal to) a pressurein the fluid drivers 312 experiencing the actuation pressure, then fluidwill simply not flow out of the corresponding tube during thatactuation.

In some embodiments, a ventricular pump may be operated in an open-loopcontrolled manner, independent of any other system state. The nature ofa ventricular pump is such that, if upstream fluid is unavailable (i.e.,is at a low pressure) or if downstream pressure exceeds a pressure inthe fluid driver 312 caused by an actuation pressure, fluid will simplynot flow through the pump, but the pump will not necessarily be damagedby continuing to apply actuation pressures to the driver. In some cases,fluid may flow in some drivers/conduits 312 and conduits 324, 326 whileno fluid flows in other drivers/conduits 312 and conduits 324, 326 inthe same pump 300. Therefore, a single actuator 350 may drive fluid atdifferent rates through the various drivers/conduits 112 and conduits324, 326 without adverse effects on the pump 300 or other parts of thesystem.

The actuator 350 may generally be configured to cycle between a “low”applied actuation pressure and a “high” applied actuation pressure.Fluid will be expelled from the fluid drivers 312 when a “high” appliedactuation pressure exceeds a fluid pressure downstream of a downstreamvalve 344. Fluid will be drawn into the fluid driver conduits 312 when apressure upstream of the upstream valve 342 is greater than a “low”pressure of the actuation fluid within the housing 310. The “high” and“low” pressures may be positive or negative in absolute terms (i.e.,relative to atmospheric conditions), and will be operational when theforegoing pressure relationships are present. Therefore, the absolutepressures applied to the actuation fluid is less important than therelative pressures as compared with expected or designed pressuresupstream and downstream of the ventricular pump housing 310 and/or fluiddriver 312.

In various embodiments, the pressure applied by an actuator 350 to anactuation fluid 320 may be an absolute positive pressure or an absolutenegative pressure. In some embodiments, an applied actuation pressuremay be cycled between a “low” positive absolute pressure and a “high”positive absolute pressure. Alternatively, an applied actuation pressuremay be cycled between a positive absolute pressure and a negativeabsolute pressure. In further embodiments, an applied actuation pressuremay be cycled between a “low” (more negative) negative absolute pressureand a “high” (closer to zero) absolute pressure.

In various embodiments, an actuator 350 may be arranged to apply anactuation pressure to a single ventricular pump housing 310 or to aplurality of ventricular pump housings 310 either simultaneously oralternately. For example, alternate application of an actuation pressuremay comprise applying actuation pressures at opposite ends of a pistoncycle, by valve configurations directing pressure to alternate conduits,or by other mechanisms. Simultaneous application of actuation pressureto multiple ventricular pumps may be accomplished by applying pressureto an actuation fluid in a conduit common to multiple branches, eachbranch leading to one or more ventricular pump housings and/or fluiddrivers.

In various embodiments, the actuation fluid may be a compressible fluidsuch as air, nitrogen, argon, or other gas or gas mixtures, or anincompressible fluid such as water, an oil, or other incompressibleliquid. If a compressible actuation fluid is used, then duringapplication of an actuation pressure to the actuation fluid, a pressureapplied to a fluid driver 312 may be lower than the actuation pressureby a pressure quantity required to overcome any resistance of the fluiddriver 312 to compression or deflection. Therefore, an excess pressure(greater than a desired pressure) may be applied to a compressible fluidin order to impart a desired pressure to the fluid drivers 312.

The ventricular pump type provides several advantages in anelectrochemical system as described herein. In addition to being alow-cost pump with very few wearable moving parts, a ventricular pumpallows for simple passive control of fluid flows based on relativepressures of fluid volumes, including gas-liquid fluid mixtures.Additionally, because a ventricular pump can control a large number(e.g., hundreds or even thousands) of parallel flows, a single pump maybe used for controlling fluid flows in a large number of independentvolumes, such as individual half-cells of an electrochemical cell-stackwhich may contain several hundred cells.

An example of operating a ventricular pump in an electrochemical systemmay be understood with reference to FIG. 1 and FIG. 2. Electrolyte 130,131 in the electrolyte capture volume 110, 112, 210, 212 may be pumpedinto the cell 100, 200 by a ventricular pump 300. The ventricular pump300 may be periodically actuated at a frequency sufficient to returnelectrolyte to the cell 100, 200 at a desired rate. For example, in someembodiments electrolyte may be returned to the cell 100, 200 at a rateroughly equal to the expected rate at which electrolyte escapes thehalf-cell chamber 232, 242 into the capture volume 110, 112, 210, 212.The outlet 118 of the capture volume 110, 112, 210, 212 may be joined toa conduit at an inlet end of the ventricular pump 300, and one or moretubes or other fluid drivers 312 may be joined to the capture volumeoutlet conduit.

Upon each actuation of the ventricular pump 300, a volume of electrolytedownstream of the capture volume outlet 118 may be driven downstreamtowards the return conduit 114, 116, 214, 216 by actuation of a fluiddriver. The fluid pressure in the return conduit 114, 116, 214, 216 maybe affected by the expansion volume 280 (if present) and the fluidpressure within the half-cell chamber 232, 242. If the pressure in thereturn conduit 114, 116, 214, 216 is less than the fluid pressureimparted by the ventricular pump actuation, then the volume of fluidfrom the tube 312 will be driven into the return conduit 114, 116, 214,216. When the ventricular pump actuation pressure is released (ordecreased), if the fluid pressure in the capture volume 110, 112, 210,212 exceeds the “low” fluid pressure in the fluid driver section 172,174, 272, 274, then a volume of fluid will flow through the upstreamvalve 221 to fill the fluid driver conduit within the ventricular pump300.

FIG. 1 and FIG. 2 schematically illustrate a single ventricular pumpfluid driver 172, 174, 272, 274 associated with each half-cellelectrolyte capture volume 110, 112, 210, 212. However, in variousembodiments a single ventricular pump fluid driver may be associatedwith any number of half-cell electrolyte capture volumes. For example,in some embodiments, all electrolyte return pump tubes in an entire cellstack may be associated with one ventricular pump fluid driver, or withone common housing volume. In other embodiments, all positive half-cellelectrolyte return pump fluid drivers may be in one ventricular pumphousing (actuated by a first common fluid volume) and all negativehalf-cell return pump tubes may be in a second housing (actuated by asecond common fluid volume). In some embodiments, a single actuator mayapply an actuation pressure to both a first actuation fluid drivingpositive half-cell ventricular pumps and a second actuation fluiddriving negative half-cell ventricular pumps. In other embodiments,fluid drivers may be bundled into various other combinations of cells orhalf-cells. In some embodiments, a “pump” or a pump component may beprovided for each individual electrochemical cell, or alternatively, foreach individual half-cell, for example, as an individual conduit or anindividual conduit section.

In various embodiments, a ventricular pump housing may comprise a volumedefined by apertures in layers of a stacked plate-and-frame cell-stackstructure. In such embodiments, a fluid driver section may be positionedwithin or adjacent to the housing so as to allow an actuation fluidwithin the housing to drive fluid within the conduit section downstreamof the fluid driver.

FIG. 3B and FIG. 3C illustrate an example embodiment planarimplementation of a ventricular pump which may be integrated into astackable cell-frames as further described below with reference to FIG.11-FIG. 12B. Although the substrate and pump features are illustrated ina horizontal plane in FIG. 3B and FIG. 3C, cell-frames and pump featuresmay be oriented in a vertical plane (or any other plane) in variousimplementations of a cell-stack.

In the example embodiment shown in FIG. 3B and FIG. 3C, a ventricularpump 360 may comprise a pump chamber 362 (which may perform a functionsimilar to the housing 310 of FIG. 3A) formed as a feature within asubstrate 364, which may be a portion of a cell-frame in a cell-stack.The pump chamber 362 comprise an in-flow (upstream) aperture 366 and anout-flow (downstream) aperture 368, each configured to receive a one-wayvalve 367, 369. FIG. 3B and FIG. 3C illustrate the one-way valves asumbrella-type valves, but any other one-way valve type may be used asdescribed herein. The in-flow (upstream) aperture 366 may be fluidicallyconnected to an in-flow (upstream) conduit 370 in the substrate 364.Similarly, the out-flow (downstream) aperture 368 may be fluidicallyconnected to an out-flow (downstream) conduit 372 in the substrate 364.

The pump 360 may also comprise a fluid driver in the form of a flexiblediaphragm 374 (although other fluid driver types may also be used asdescribed herein). In the illustrated embodiment, a cover 376 may alsobe provided to transmit a compressive force to a periphery of thediaphragm 374 against the substrate when the assembly is compressed. Thecover 376 may also comprise various openings 377, channels 378, or otherstructures to allow actuation fluid to flow around the cover 376 tocontact the diaphragm 374. In some embodiments, a cover 376 may compriseother structures such as a solid disk with holes or slots to allowactuation fluid to pass therethrough. The cover 374 may be made of amaterial more rigid or less compressible than the diaphragm 374 so as toensure a seal while maintaining actuation fluid flow channels.

A gasket or O-ring 380 may also be provided to seal the pump chamber 362from surrounding volumes when compressed against a channel 381 in thesubstrate 364. In various embodiments, the gasket or O-ring 380 may sealagainst an adjacent planar structure (not shown in FIG. 3B) such as anadjacent cell-frame or a cover-sheet pressed against the cover 376 andthe O-ring 380.

FIG. 3B also illustrates a first actuation fluid conduit 382 and asecond actuation fluid conduit 384. In some embodiments, the actuationfluid conduits 382, 384 may be used as in-flow (upstream) and purgeconduits respectively. For example, actuation may be performed bydriving actuation fluid into the first conduit 382 while flow out of thesecond actuation conduit 384 is prevented, thereby causing a pressureincrease in both conduits and in the pump housing 362 above thediaphragm 374. In such an example, when actuation is complete, pressuremay be decreased by allowing flow out of the second actuation fluidconduit 384. In some embodiments, either one or both conduits 382, 384may be used to apply an actuation pressure to the actuation fluid overthe diaphragm 374, and/or pressure may be released through eitherconduit 382, 384. In some embodiments, a single actuation fluid conduit366 or 368 may be present, omitting a second conduit.

FIG. 3B further shows a driven-fluid in-flow (upstream) conduit 370through which a driven fluid (e.g., electrolyte in some embodimentsherein) may flow into the pump chamber 362. The driven fluid may alsoflow out of the pump chamber 362 via a driven-fluid out-flow(downstream) conduit 372. In various implementations, one or more of thedriven-fluid in-flow conduit 370, the driven-fluid out-flow (downstream)conduit 372, the in-flow (upstream) aperture 370 and the out-flow(downstream) aperture 372 may be located at regions of the substratedistant from the pump chamber 362, while being fluidically connected tothe pump chamber 362 by conduits or channels. An example of such aconfiguration is described herein with reference to FIG. 11-FIG. 12B.

FIG. 3C is a cross-section of the assembled ventricular pump 360 of FIG.3B through section line C-C. The assembled pump of FIG. 3C furtherincludes a top cover-sheet 390 sealed against the O-ring 380 so as toenclose the pump chamber 362 and the actuation fluid conduits 382, 384.A bottom cover-sheet 392 is included to enclose and contain the one-wayvalves 367, 369 and the driven-fluid in-flow (upstream) conduit 370 andthe driven-fluid out-flow (downstream) conduit 372. In some embodiments,the actuation fluid 382, 384 conduits may be continuously connectedthrough all cell-frames of a cell-stack (i.e., the conduits 382, 384 maypass through an opening in the top cover sheet or adjacent cell-frame).

When actuation fluid is driven in the actuation fluid conduit 382towards the pump chamber 362, pressure (and/or fluid flow) may betransmitted through the actuation fluid conduit 382, through the channel378 in the cover 376, and into contact with the actuation-side (top sideas shown) of the diaphragm 374. Under the influence of the actuationpressure, the diaphragm 374 may be deflected downwards towards theone-way valves 369, 370, thereby increasing fluid pressure in the pumpchamber 362 below the diaphragm 374. The out-flow (downstream) one-wayvalve 369 may open under influence of the increased pressure, allowingfluid to flow out of the pump chamber 362 through the driven-fluidout-flow (downstream) conduit 372.

When the actuation pressure is released or reversed, pressure in thedriven-fluid in-flow (upstream) conduit 370 may exceed pressure in thepump chamber 362 below the diaphragm 374, thereby allowing driven-fluidto flow into the pump chamber 362 through the in-flow (upstream) one-wayvalve 367.

Volume Expansion System

As shown in FIG. 2, in some embodiments of an electrochemical system asdescribed herein, each cell 100, 200 may be configured with an expansionvolume 280 configured to allow volumetric expansion of fluids within acell volume while passively controlling cell pressures. In someembodiments, an expansion volume 280 may also be configured to provide aregion at which the fluid pressures of the positive electrolyte 131 andthe negative electrolyte 132 of a cell are “tied together” in the sensethat a lower-pressure electrolyte may directly decrease pressure of thehigher-pressure fluid within the expansion volume and conduits joinedthereto.

When an electrolytic cell 100, 200 configured for gas-generatingelectrochemical reactions is initially powered on from an idle state,gas bubbles are rapidly formed and displace liquid electrolyte 130, 131.In a volume of unchangeable size, this increase in gaseous fluid willcause the fluid pressure in the half-cell to rapidly increase.Differences in the rate at which gas is produced in each half-cell cancause substantial cross-separator pressure differences, which can driveliquid electrolyte and/or gas bubbles across the separator or aroundseals, causing gas crossover and/or leakage. Additionally, if anelectrochemical reaction in the cell is exothermic, gas and liquidelectrolyte in the half-cell chamber will tend to expand. If the volumeis constrained, the thermal expansion will instead increase the fluidpressure in the half-cell chamber. In conventional electrolyzers, suchpressure swings are managed by flowing electrolyte through each cell,thereby carrying away excess fluid volume.

By providing each cell with an expansion volume into which a fluid mayexpand, the pressure within each half-cell may be passively controlledwithout the need to flow electrolyte through the cell. Allowingelectrolyte from both half-cell chambers to expand into a common volumemay allow for passive equalization of pressures in the half-cells,thereby minimizing cross-separator pressure differentials.

In the example of FIG. 2, the expansion volume 280 is illustrated as anexpandable bellows 283 which resists expansion due to a spring forcerepresented schematically by a spring 281. In various implementations,an expansion volume may be made of materials and structures capable ofcontaining a fluid volume while allowing expansion. For example, anexpansion volume may comprise a balloon-like structure, one or moreflexible diaphragms, one or more bellows, or other structures.

In some embodiments, an expansion volume 280 may be configured to exerta degree of resistance to expansion, forcing at least some increase inpressure as a fluid volume expands. This is illustrated schematically bythe spring 281 in FIG. 2. In various embodiments, a resistance toexpansion may be implemented as a spring-constant of an expandablemember such as a bellows, diaphragm, balloon, etc. In some embodiments,resistance to expansion may be controlled through the use of a workingfluid (liquid or gas) on the opposite side of an expansion volumeboundary (e.g., a diaphragm or balloon wall). In some embodiments, aresistance to expansion may be a function of expansion displacement,thereby applying an increasing resistance to expansion as the volumeexpands. For example, resistance to expansion may be a linear functionor non-linear function (e.g., geometric, step-function, exponential,etc.) of a linear, area, or volumetric measure of expansion.

In some embodiments, an expansion volume may be divided into separateregions or compartments configured to prevent mixing of positiveelectrolyte 131 and negative electrolyte 130 but allowing bothelectrolytes to expand together. For example, a flexible expandablediaphragm may be used to separate positive and negative electrolytes. Inother examples, an expansion volume may be divided into two chambers bya non-flexible divider. In such embodiments, each expansion volumechamber may be separately joined to respective half-cell chambers by oneor more fluid conduits.

In still further embodiments, a cell may be configured with separate andindependent expansion volumes for the positive electrolyte 131, 231 andthe negative electrolyte 130, 230. For example, in some embodiments, anelectrolyte return conduit 114, 214, 116, 216 may be made of or joinedto an expandable conduit such as a section of a resilient expandabletubing or other expansion volume structures such as those describedabove.

In some embodiments, whether or not electrolytes 131, 130 are joined ina common pressure volume such as an expansion volume 280, a separateregion of common pressure may be provided in a cell 100, 200. Forexample, in some embodiments, the positive headspace 134, 234 may bejoined to a negative headspace 144, 244 by a common make-up liquidsupply conduit 179, 279 or drip chamber (described further below).Alternatively, a pressure region common to the positive and negativeelectrolytes from a single cell may be provided at any other region of acell. In various embodiments, a common pressure region may be configuredto allow or prevent mixing of positive and negative electrolytes. FIG.13, described in further detail below, illustrates an example expansionvolume implemented in a substantially planar cell-frame as a componentof a cell-stack of multiple electrochemical cells.

Gas Collection System

With reference to FIG. 2 (but equally applicable to examples in otherfigures), each electrochemical half-cell 232, 242 in an electrochemicalsystem may be in fluid communication with a gas removal manifold 222,224 in which a gas removal fluid 252 may flow. Gas escaping a half-cellchamber 232, 242 via one or more fluid escape elements 260, 261 maybuild pressure within a gas-liquid separator 282, 284 in communicationwith the gas removal manifold, which may be maintained at a pressurelower than a half-cell pressure and lower than a make-up liquid supplymanifold pressure as described above. Gas contacting the gas removalliquid 252 may dissolve and/or form bubbles in the gas removal liquid252 and may then be carried away from the cell 200 by the flowing gasremoval liquid 252.

In some embodiments, the gas removal liquid 252 may be the same liquiddelivered into the cell 200 via the supply manifold 278 to replaceliquid consumed in the electrochemical reactions within the cell 200.For example, in embodiments in which the electrochemical system is analkaline electrolyzer, the gas removal liquid 252 and the make-up liquidmay be (at least predominantly) deionized water. In other embodiments,the gas removal liquid 252 may be a different liquid than that suppliedto the cell. The gas-removal liquid is preferably an electricallynon-conductive liquid, preferably no more conductive than deionizedwater as defined herein. For example, the gas removal liquid 252 may bean aqueous solution, a molten salt, an ionic liquid, an oil, anon-aqueous electrolyte solution, etc. Optionally, a gas-removal liquidmay have a different, or substantially different, composition comparedto any of the electrolytes used in half-cell(s). Optionally, forexample, the gas-removal liquid comprises the same solvent as used in anelectrolyte of the cell(s), but is free, or substantially free, of thesolute(s) used in the electrolyte(s). A gas-removal liquid can compriseone or more chemical species, such as one or more liquid species, andoptionally one or more dissolved species. Generally, a gas-removalliquid corresponds to a volume of liquid used for (optionally,primarily, essentially, or only used for) removal of gas from a region,such as a gas-removal manifold, such as by dissolution and/or bubbleentrainment of the gas in the gas-removal liquid, optionally followed bytransport of the gas removal liquid away from said region.

In some embodiments, a gas-removal manifold may contain substantiallyonly the produced gas (i.e., a gas-removal liquid may be omitted).However, the use of a liquid gas-removal medium (or, gas removal liquid)provides several advantages. For example, any electrolyte mist travelingwith the gas may be dissolved in or incorporated into the gas removalliquid 252 and thus removed from the gas stream, thereby washing the gasof electrolyte impurities. Also, gas bubbles entering the gas removalliquid may cause gases such as CO₂ or other gas impurities dissolved inthe gas-removal liquid to be removed from the liquid (e.g., a spargingeffect). The gas-removal liquid may also beneficially prevent persistentbuildup of electrolyte deposits on walls of the gas removal manifold222, 224 or other piping or conduits through which the gas removalliquid flows.

In some embodiments, the gas removal liquid 252 may be water, such asdeionized water. In some embodiments, the gas-removal liquid in thepositive gas-removal manifold 224 and the gas-removal liquid in thenegative gas-removal manifold 222 may be the same liquid from a commonsource. In some embodiments, the gas-removal liquid 252 may be the sameliquid as that supplied to the cell via the make-up liquid supplymanifold 278. In other embodiments, make-up liquid in the positivegas-removal manifold 224 may be a different composition and/or from adifferent source than gas-removal liquid in the negative gas-removalmanifold 222. Similarly, the make-up liquid supplied to the supplymanifold 278 may be of a different composition and/or from a differentsource than make-up liquid used in either or both of the positive 224and negative 222 gas-removal manifolds.

In some embodiments, fluid pressures and flows in the gas removalmanifold may be applied or maintained by one or more pumps, such as apositive displacement pump, a ventricular pump, or any other pump type,including those described elsewhere herein. In some embodiments, a pumpsupplying a gas-removal liquid to a gas-removal manifold may becontrolled by one or more electronic controllers operating in aclosed-loop control system based on a pressure sensor or a flow sensor(or other sensor) within or in communication with the gas-removalmanifold. In some embodiments, a pressure of gas-removal liquiddelivered to both gas removal manifolds may be controlled by a commonpump delivering gas-removal liquid to a stack of electrochemical cells.In some embodiments, the pressure of the gas removal manifolds may becontrolled by backpressure regulators at a region downstream of the exitfrom a cell stack.

In some embodiments, the pressure of a positive gas-removal manifold124, 224 may be controlled independent of a pressure of a negativegas-removal manifold 122, 222. In some embodiments, it may be desirableto maintain both the positive and negative gas removal manifolds atsubstantially the same pressure. However, in practical terms, actualpressures in the gas removal manifolds are likely to vary slightly fromtarget control pressures, meaning some variation is to be expectedbetween a positive gas removal manifold pressure and a negative gasremoval manifold pressure. As described above, suitable fluid escapeelements may dampen such variations, minimizing their effect onpressures in the half-cell chambers.

Make-Up Liquid Supply

In various embodiments, a make-up liquid may be passively or activelydelivered to a cell 200 via a supply manifold 278. For example, in someembodiments of a passive delivery configuration, a make-up supplymanifold 278 may be maintained at a constant fluid pressure that isapproximately equal to a steady-state operating pressure of a cell orhalf-cell chamber into which make-up liquid is to be delivered. Aone-way check valve 176, 276 at a make-up liquid supply outlet mayprevent make-up liquid from being delivered when a cell or half-cellpressure exceeds the supply manifold pressure. When the pressure in thecell or half-cell chamber drops (e.g., due to fluid exiting a half-cellvia a fluid escape element) below the supply manifold pressure, aquantity of make-up liquid may be delivered through the check valve 176,276 until the pressures are equalized and the one-way valve closesagain.

The composition of a make-up liquid may depend on specifics of areaction to be performed as described elsewhere herein. For example, inthe case of a water-splitting alkaline electrolyzer, a make-up liquidmay consist essentially of deionized water, possibly with a smallconcentration of an alkaline hydroxide. For simplicity of description,the make-up liquid may be referred to herein simply as “water” althoughother make-up liquid compositions may be used instead of or in additionto water.

As shown schematically in FIG. 1 and FIG. 2, a make-up liquid may besupplied to a cell 100, 200 from a supply manifold 178, 278 via a supplyconduit 179, 279 which may include a one-way valve 176, 276. The one-wayvalve 176, 276 may provide several benefits.

As described elsewhere herein, the fluid pressure within a cell maychange substantially depending on a stage of operation. Nonetheless, ata “steady state” of operation, the pressure within a half-cell chambermay fluctuate only minimally. Therefore, an average cell pressure during“steady state” operation may be established empirically and/or bydesign. As used herein, “steady state” operation refers to a stage ofoperation during which operating variables of the cell (e.g., voltage,pressure, temperature, etc.) fluctuate minimally, or no more than about10%.

In particular, a steady state pressure of the cell or a half-cellchamber is a pressure that varies by no more than about 20%, in someembodiments no more than about 10%, in some embodiments no more thanabout 5%, in some embodiments less than about 3%, and in someembodiments less than about 1%. In some embodiments, a steady-statepressure is a pressure that varies by less than about 2 bar, less thanabout 1 bar, less than about 0.5 bar, less than about 0.3 bar, less thanabout 0.2 bar, less than about 0.15 bar, less than about 0.1 bar, orless than about 0.07 bar. In some embodiments, a steady state half-cellpressure may vary by less than about 5 psi, in some embodiments lessthan about 3 psi, in some embodiments less than about 2 psi, and in someembodiments less than about 1 psi. A steady state pressure may be apressure that varies by less than about 2 atm, less than about 1 atm, orless than about 0.5 atm, less than 0.25 atm or less than 0.05 atm.

At a steady state of operation, the fluid pressure within the cell willalso tend to have minimal variation and may be referred to as a “steadystate pressure” of the cell or a half-cell chamber. In some embodiments,the half-cell pressures may vary minimally from one another duringsteady state operation, so the steady state cell pressure may also besubstantially the same as the steady state pressure within bothhalf-cells.

In addition to a “steady state” of operation, some embodiments of anelectrochemical system may experience an “idle” state, a “startup”state, and a “shutdown” state. Depending on an application of theelectrochemical system, the rate or frequency at which a system isrequired to cycle from start up, run at steady state, shut down, andidle may vary substantially. For example, some embodiments of anelectrolyzer used to produce hydrogen as an energy store may be startedup, run, shutdown, and idled several times per day. In some embodiments,an electrolyzer may be operated at various currents between minimum andmaximum operating currents for which the electrolyzer is designed. Forexample, an electrolyzer supplied with power from a solar array mayexperience rapid changes in supplied current due to moment-to-momentvariation in power generated by the solar panels due to changing cloudcover or other conditions. Such changes in current may cause momentarychanges in pressure within a cell or half-cell.

In some embodiments, the make-up liquid in the supply manifold 178, 278may be maintained at a pressure that is approximately equal to orslightly greater than an expected steady-state pressure within thehalf-cell into which the make-up liquid is delivered. This allows forpassive delivery of make-up liquid to the cell 100, 200 when thepressure in the half-cell chamber 232, 242 drops below the pressuremaintained in the supply manifold 178, 278.

On the other hand, when a pressure in the half-cell chamber 232, 242exceeds a pressure in the supply manifold 178, 278, gas and electrolyteare prevented from flowing back into the supply manifold by the one-wayvalve 176, 276. Any one-way valve may be used, including the variousone-way valve examples described elsewhere herein.

In various embodiments, the pressure in the supply manifold may bemaintained at a pressure that is approximately equal to a median steadystate fluid pressure in the cell. In embodiments in which anelectrochemical system is operated at an absolute pressure higher thanatmospheric pressure, the pressure of the supply manifold make-up liquidmay be maintained at a desired absolute pressure or at a desiredrelative pressure defined with reference to an expected, applied, ormeasured cell pressure.

Although FIG. 1 and FIG. 2 illustrate a supply manifold 178, 278delivering a make-up liquid to the negative half-cell, the make-upliquid may alternatively be added to the positive half-cell, or to bothhalf cells. In alternative configurations, a cell may be arranged so asto allow for make-up fluid to be added to an inter-electrode spacebetween the positive and negative electrodes 102, 104, 202, 204.

In some embodiments, the supply manifold pressure may be applied ormaintained by a pump, such as a positive displacement pump, aventricular pump, or any other pump type, including those describedelsewhere herein. In some embodiments, a pump supplying make-up liquidto the supply manifold may be controlled by an electronic controlleroperating in a closed-loop control system based on a pressure sensor ora flow sensor. In still other embodiments, a supply manifold pressuremay be applied or maintained by any other mechanism capable of applyingpressure to a fluid such as an elevated supply reservoir, compressedgas, or others. In some embodiments, a particular pressure may bemaintained or regulated through the use of a compressed gas and/orbackpressure regulators.

Fluid Pressure Controls

FIG. 4 is a schematic illustration of a fluid management system 400 fordelivering make-up liquid to electrochemical cells 410 in a cell stack412 and for removing produced gases from the cells 400 with agas-removal liquid. In the system of FIG. 4, the make-up liquid and thegas-removal liquid may be substantially the same liquid, such asdeionized water. For simplicity, the term “water” will be used todescribe the fluid flows, but the actual composition of the gas-removalliquid and/or the make-up liquid may be different as described elsewhereherein.

As shown in FIG. 4, a first pump 420 may deliver water from a storagetank 422 to an inlet 424 of a supply manifold 426 of a cell-stack 412.The supply manifold 426 may deliver water to each cell 410 of thecell-stack 412 as described herein. In some embodiments, the first pump420 may be controlled by an electronic controller based on measurementsfrom one or more sensors 428. In some embodiments, a sensor 428 maycomprise one or more pressure sensors, and the controller may containdigital or analog programming to maintain the water entering the stacksupply manifold 426 within a desired range of pressure.

Alternatively, a sensor 428 may comprise one or more flow sensors (e.g.,a sensor for detecting a volumetric flow rate or a mass flow rate) andthe controller may contain digital or analog programming to maintain aflow rate of water flowing into the supply manifold 426 within a desiredrange. In some embodiments, a controller may control the first pumpbased on both pressure and flow sensors. In still other embodiments, thesensor 428 may be or comprise a back-pressure regulator configured tocontrol a pressure in the supply manifold 426 by applying aback-pressure at a point down-stream of the cell stack 412.

In some embodiments, water exiting the supply manifold 426 may be pumpedby a second pump (not shown) into the gas-removal manifolds 432, 434.Alternatively, the water exiting the supply manifold 426 may flow intothe gas removal manifolds under pressure created by the first pump 420.In some embodiments, the water conduit may be divided into a positivegas-removal manifold 432 and a negative gas-removal manifold 434 at anentrance 436 to the cell-stack 412. In some embodiments, the second pump(if present) may be controlled by an electronic controller based onmeasurements from one or more sensors 438 (e.g., a pressure sensorand/or a flow sensor as described above) at the inlet to the gas-removalmanifolds 432, 434. Alternatively, a sensor 438 may comprise aback-pressure controller configured to maintain pressure within the gasremoval manifolds within a desired range of pressure.

Water passing through the gas-removal manifolds 432, 434 will collectgas produced by the cells 410 and may also collect a small quantity ofelectrolyte in the form of droplets, mist, or vapor. After exiting thegas-removal manifolds 432, 434, the separate mixtures of water andfluids collected from the cell-stack 412 may be directed to productseparation, filtration, purification, or other treatment systems wherethe water may be treated prior to being directed into the storage tankand/or being returned to the cell-stack 412. In some embodiments, thestorage tank, treatment systems, or other elements may be omitted.

Electrochemical systems comprising features described herein may beconfigured to maintain pressure relationships between various fluidpressure regions primarily under passive control. With reference to FIG.2 (but also applicable to other configurations), pressure relationshipsin a cell 200 may be described with reference to four pressure regions.A first pressure region is defined as the full-cell volume whichincludes the positive and negative half-cell chambers 232, 242, theelectrolyte return conduits 214, 216, and the expansion volume 280. Asecond pressure region is defined as the negative gas-collection volume282, the negative fluid escape element 260 defining a boundary betweenthe first pressure region and the second pressure region. A thirdpressure region is defined as the positive gas-collection volume 284,the positive fluid escape element 261 defining a boundary between thefirst pressure region and the third pressure region. A fourth pressureregion is defined as the make-up liquid supply manifold 278, and thesupply inlet valve 276 defining a boundary between the fourth pressureregion and the first pressure region. In some embodiments, additionalpressure regions may also exist. For example, a ventricular pumpactuation fluid may define a fifth pressure region, and a working fluidestablishing resistance to the expansion volume may define a sixthpressure region.

In some embodiments, pressure relationships between the above-definedpressure regions may be maintained by actively controlling pressure inonly some of the regions, allowing components operating in response topressure differences to passively maintain pressure relationships. Asdescribed above, a pressure in a make-up liquid supply manifold 278 maybe maintained at a constant pressure that is approximately equal to orslightly greater than a steady-state fluid pressure in the full-cell 200(or in the half-cell 244 into which make-up liquid is delivered). Thepositive and negative gas removal manifolds 222, 224 may be maintainedat a pressure lower than a minimum pressure in the full-cell orhalf-cells, thereby ensuring that fluid will flow out of the half-cellchambers as described above. The fluid pressure in the full-cell mayfluctuate depending on a stage of operation of a cell 200.

FIG. 5A-FIG. 5D provide schematic illustrations of the flow rate ofmake-up fluid entering a cell (e.g., 200 in FIG. 2) from a supplymanifold 278, a volume of fluid in the full-cell (i.e., a degree ofexpansion of the expansion volume 280), and relative pressures of thefour above-defined pressure regions at four stages of operation of thecell. The Charts of FIG. 5A-FIG. 5D illustrate relative values (notnecessarily to scale) and therefore do not include numerical values.Pressure of the four pressure regions are shown relative to the leftvertical axis, while a flow rate of make-up liquid is shown relative toa separate right-side vertical axis. Pressures in each of the fourpressure regions and make-up liquid flow rate are shown at differentvalues of full-cell fluid volume which is represented on the horizontalaxis.

All of FIG. 5A-FIG. 5D show the full-cell pressure increasing as theexpansion volume increases, with the full-cell pressure intersecting amake-up liquid supply pressure (which may be maintained constant at allexpansion volumes) at a point at or near zero volume expansion. Thepositive and negative gas removal manifolds may also be maintained atconstant pressures at all expansion volumes. In some embodiments, thepositive gas removal manifold pressure may be maintained substantiallyequal to the negative gas removal manifold pressure. The positive andnegative gas removal manifold pressures may also be intentionally heldat different pressures, with either a positive gas-removal liquid or anegative gas-removal a liquid held at a higher pressure relative to theother. The positive and negative gas removal pressures are shown in FIG.5A-FIG. 5D as different lines in order to clearly show both lines.

FIG. 5A represents pressures and make-up liquid flow rate at an “idle”state. At the “idle” state, the pressure regions have been pressurizedto desired relative (and/or absolute) pressures, but no power is beingdelivered to the cell and therefore no gas is being generated. At theidle state, electrolyte return pumps 272, 274 may be operated to returncaptured electrolyte from the electrolyte capture volumes 210, 212 tothe half-cell chambers 242, 232 and/or the expansion volume 280. As aresult of the returning electrolyte flow, electrolyte in one or bothhalf-cells may tend to flow through the fluid escape elements 260, 261from the half-cell chambers 242, 232 into the electrolyte capturevolumes 210, 212.

As shown in FIG. 5A, at the idle state the full-cell fluid volume willbe at its minimum (i.e., minimal or no expansion of the expansion volume280), and thus the full-cell fluid pressure is greater than or equal tothe pressure in the make-up liquid supply manifold 278 and therefore theflow rate of make-up liquid into the cell is zero.

Before startup, the gas-liquid separators 282, 284 may bepre-pressurized above the controlled liquid pressure in the removalmanifolds 432, 438. Also before startup, the half-cell chambers may bepre-pressurized to a desired minimum cell operating pressure and/orother regions may be pre-pressurized to desired pressures.

When the cell is started, the formation of gas in the cell will cause avolumetric expansion of the fluid within the half-cell chambers andaccommodated by deflection of expansion volume, accompanied by anincrease in pressure due to resistance imparted by the expansion volumeas described above. Pressure is allowed to build in the cell as fluidexpands into the expansion volume, but pressure will increase as gas isproduced until gas and electrolyte escape through fluid escape element.Pressure in the gas removal manifolds may be controlled to beapproximately equal to a minimum pressure expected in the cell, meaninggas pressure will build in the gas-liquid separator until gas enterssolution and/or forms bubbles in the gas-removal fluid flowing in thegas-removal manifolds.

During the “startup” state illustrated in FIG. 5B, the cell fluid volumemay increase (as shown by the arrow) due to gas-forming reactions in oneor both half-cell chambers, and the increased fluid volume may expandinto the expansion volume, thereby increasing the full-cell pressure ofthe liquid and gas in the half-cell chambers. Because full-cell pressureexceeds the make-up liquid supply pressure, no make-up liquid will tendto flow during the startup period. As fluid leaves the half-cellchambers 242, 232 into the electrolyte capture volumes 210, 212 and gasremoval manifolds 222, 224, the volume and pressure of the fluid in thehalf-cells will fall.

As represented in FIG. 5C, once the cell reaches a steady-state runningoperation, the cell fluid volume will return to a minimum, at whichpoint make-up liquid may flow. During steady-state operation, the totalvolume of fluid in the cell and/or the fluid pressure within the cellwill tend to oscillate between a low-pressure point at which make-upfluid may flow and a slightly higher-pressure point at which thefull-cell pressure exceeds the make-up liquid supply pressure at whichpoint no make-up fluid flows.

As illustrated in FIG. 5D, when the cell is shut down, the cessation ofgas production will cause the full-cell pressure and volume to quicklyfall back towards the “idle” state of FIG. 5A, and the make-up liquidflow rate will fall to zero as the pressure oscillations drivingoccasional pressure differences allowing fluid flow dissipate.

One-way check valves, such as the valve 276 separating the make-upliquid supply manifold and the half-cell volume 242, typically require apressure difference exceeding a “cracking pressure” before they willopen to allow uni-directional fluid flow. Various examples herein aredescribed assuming “ideal” check valves which are shown requiring zerocracking pressure. In practical implementations, one-way check valveswill have non-zero cracking pressures, and pressure differences betweenthe various pressure regions will need to be sufficient to overcome thecracking pressures before fluid will flow. In some embodiments, checkvalve cracking pressure may be chosen based on desired performancecharacteristics.

In some embodiments, flow of process water in electrochemical systemsdescribed herein (including low-flow ion-exchange electrolyzers (LFIE)and other electrolyzers as described herein) may be substantiallyentirely controlled by monitoring and managing pressure at variouspoints in the system. For example, in some embodiments, flow of processwater through an electrochemical cell-stack may be controlled bypressure regulators affecting fluid pressure at three points: aprocess-water supply manifold, a positive gas-removal manifold, and anegative gas-removal manifold.

As shown in FIG. 14A and FIG. 14B, pressure in a process water supplymanifold 1440 may be controlled by a back-pressure regulator 1464located downstream of an inlet to the supply manifold 1440. Inalternative embodiments, pressure in the supply manifold 1440 may becontrolled by a pressure regulator located upstream of the supplymanifold 1440. Alternatively, pressure in the supply manifold 1440 maybe controlled by operation of the pump 1452 in a closed-loop oropen-loop control system.

In other embodiments, the pump 1452 may be operated in an un-controlledor minimally-controlled manner by simply delivering a sufficient flow ofprocess water to the supply manifold 1440 for the pressure regulators1464, 1466, 1642 to control respective pressure by regulatingback-pressure.

Similarly, in some embodiments, pressure in the first-gas removalmanifold 1422 may be controlled by a back-pressure regulator 1462located downstream of the first gas-removal manifold 1442, and pressurein the second gas removal manifold 1444 may be controlled by aback-pressure regulator 1466 located downstream of the manifold 1444.

Example Configurations

The various systems and sub-systems described above may be modified,omitted, or differently configured in various embodiments ofelectrochemical systems. Some examples of such configurations aredescribed below with reference to FIG. 6-FIG. 18. The examples of FIG.6-FIG. 18 (or portions thereof) may be variously combined with oneanother or with other configurations or embodiments described herein.

FIG. 6 represents an alternative configuration in which make-up liquidis passively delivered into both half-cell chambers simultaneously. FIG.6 schematically illustrates an electrochemical cell 600 with a positivehalf-cell chamber 632 and a negative half-cell chamber 642 separated bya separator 606, and being configured to retain electrolyte 630, 631within the cell 600 or half-cell chambers 632, 642. The system of FIG. 6differs from the embodiments of FIG. 1 and FIG. 2 in that the gasremoval volume and the electrolyte capture volume are a singlecoincident volume 686, 684. In some embodiments, the fluid escapeelement 665, 667 may be a membrane, e.g., a hydrophobicphase-discriminating membrane that substantially prevents thetransmission of liquid electrolyte while allowing gas to escape into thegas removal liquid 652 carried in the gas removal manifold 622, 624. Anyelectrolyte 630, 631 that does escape through the membrane 665, 667,either in liquid or vapor form, may be returned to the cell via themake-up liquid supply manifold 678.

FIG. 6 also schematically illustrates a modified make-up liquid supplysystem 670 comprising a drip-feed 672 fed by a supply manifold 678.Notably, the drip-feed 672 omits the one-way valve of the embodiments ofFIG. 1 and FIG. 2, thereby supplying a constant drip-fed flow of make-upliquid from the supply manifold 678 in which make-up liquid 671 may bemaintained at a controlled pressure.

The make-up liquid supply system 670 of FIG. 6 also includes a dripreservoir 674 that is fed from the drip-feed 672. Make-up liquid 671 maybe directed from the drip reservoir 674 to the cell 600 by a supplyconduit 676. As suggested above, the make-up liquid 671 may contain asmall concentration of electrolyte that may have escaped the cell 600.In various embodiments, make-up liquid may be driven from the dripreservoir 672 into the cell 600 by gravity (e.g., hydrostatic headpressure created by locating the drip reservoir 674 vertically above thecell 600), by one or more pumps, or by pressure within the dripreservoir 674 established by a fluid pressure in the supply manifold 678and/or in the reservoir 674 itself.

In some embodiments, as shown in FIG. 6, the supply conduit 676 may bejoined to the cell 600 adjacent to a cross-over region 691 providingfluid communication between the negative electrolyte 630 and thepositive electrolyte 631. This may allow a degree ofpressure-equalization between the positive 631 and negative 630electrolytes as described above and may allow for make-up liquid to beequally delivered to both half-cell chambers 632, 642. In someembodiments, the pressure at the cross-over region 691 may slightlyexceed the steady-state pressure in the half-cell chambers 632, 642(e.g., as established by a controlled pressure in the reservoir 674and/or the supply manifold 678), thereby generally minimizing cross-overof electrolyte from one half-cell chamber to the other while alsominimizing pressure differences between the half-cell chambers.

In a cell-stack based on the system of FIG. 6, each cell in thecell-stack may include half-cell chambers 642, 632, a separator 606,electrodes 602, 604, fluid escape elements 665, 667, gasremoval/electrolyte capture volumes 686, 684, drip reservoir 674, dripfeed 672, and supply conduit 676. The supply manifold 678 and thegas-removal manifolds 622, 624 may be joined to all other cells in thestack and to additional processing equipment, for example as describedherein with reference to FIG. 4. In some embodiments, fluid flow in themake-up liquid supply conduit may be driven by a single pump actuator(e.g., a ventricular pump actuator) joined to make-up liquid supplyconduits in several (or all) cells of a cell-stack.

FIG. 7 schematically illustrates an alternate configuration of a cell700 in which make-up liquid 771 (which may contain some electrolyte) isdriven into an inter-electrode space 711 between the negative 702 andpositive 704 electrodes. In the configuration of FIG. 7, each electrode702, 704 may have a gas-removal membrane 723, 725 affixed to an outerside of the electrode. Each electrode 702, 704 may also comprise aseparator membrane 706, 707 on an inner side facing the inter-electrodespace 711.

As in FIG. 1 and FIG. 2, the cell 700 of FIG. 7 may include separateelectrolyte capture volumes 710, 712 and gas removal volumes 786, 788,and electrolyte return conduits 714, 716 may direct captured electrolyteinto the inter-electrode space under the force of one or more pumps 772,774 such as those described above. While fluid escape elements are notshown in FIG. 7, any fluid escape elements may be used in combinationwith a cell such as that shown in FIG. 7.

As electrolyte and make-up liquid are driven into the inter-electrodespace 711, pressure may build, and electrolyte may drip through driptubes 760, 761 extending from the inter-electrode space to the half-cellchambers 742, 732 filled with electrolyte 730, 731. In some embodimentsdrip tubes 760, 761 may be constructed similarly to egress channels orother series or parallel fluid escape elements described elsewhereherein above.

In a cell-stack based on the system of FIG. 7, each cell in thecell-stack may include half-cell chambers 742, 732, separator membranes606, 707, electrodes 702, 704, drip tubes 760, 761, electrolyte capturevolumes 710, 712, electrolyte return conduits 714, 716, gas removalvolumes 786, 788, drip reservoir 774, drip feed 772, and supply conduit776. The supply manifold 771 and the gas-removal manifolds 722, 724 maybe joined to all other cells in the stack and to additional processingequipment, for example as described herein with reference to FIG. 4. Insome embodiments, fluid flow in the make-up liquid supply conduit may bedriven by a single pump actuator (e.g., a ventricular pump actuator)joined to make-up liquid supply conduits in several (or all) cells of acell-stack.

FIG. 8 schematically illustrates a cell 800 which combines features ofthe cell 700 of FIG. 7 with features allowing for gas-cooling of thecell 800. The cell 800 of FIG. 8 comprises a negative electrode 802 witha separator membrane 806 on an inner side and a hydrophobic membrane 823on an outer side and a similarly configured positive electrode 804,separator membrane 807 and hydrophobic membrane 825. Gases produced ateach electrode 802, 804 may pass through the corresponding hydrophobicmembrane 823, 825 into a gas-flow space 854, 856.

A cooling gas 855, 857 may be directed from an inflow manifold 856, 858through the gas-flow space 854, 856 where it will be joined with gasproduced at the corresponding electrode 802, 804. The combined gasstream may then flow into the corresponding gas removal manifold 822,824. In some embodiments, the inflow manifold 856, 858 may receive gascirculated through all cells of a cell-stack or multiple cell-stacks.

In some embodiments, the gas-flow spaces 854, 856 may be maintainedpredominantly liquid-free (except for liquid electrolyte that may flowthrough the drip tubes 860, 860 or that may seep through the membranes823, 825) by phase discriminatory hydrophobic membranes 823, 825.Alternatively or in addition, the gas flow spaces 854, 856 may bemaintained substantially liquid-free by maintaining a gas pressure inthe gas-flow spaces 854, 856 that exceeds (or is equal to) a pressure ofthe liquid electrolyte in the inter-electrode space 811.

The cell 800 of FIG. 8 may also include fluid egress channels 860, 861extending from within the inter-electrode space 811 to the gas-flowspaces 854, 856. Electrolyte 830 may escape from the inter-electrodespace 811 to the gas-flow spaces 854, 856 via either the egress channels860, 861 or via leakage through the hydrophobic membranes 823, 825.Electrolyte 830 that escapes from the inter-electrode space 811 (byeither path) may be collected in an electrolyte capture volume 810, 812at the bottom of a corresponding gas-flow space 854, 856. Capturedelectrolyte may be returned to the inter-electrode space 811 under powerof one or more pumps 872, 874, which may include a ventricular pump orother pump types as described above.

In a cell-stack based on the system of FIG. 8, each cell in thecell-stack may include gas-flow spaces 854, 856, separators 806, 807,membranes 823, 825, electrodes 802, 804, fluid escape elements 860, 861,electrolyte capture volumes 810, 812, drip chamber 874, drip feed 872,supply conduit 876, and electrolyte return conduits. The supply manifold878, gas inflow manifolds 856, 857 and the gas-removal manifolds 822,824 may be joined to all other cells in the stack and to additionalprocessing equipment, for example as described herein with reference toFIG. 4. In some embodiments, fluid flow in the make-up liquid supplyconduit may be driven by a single pump actuator (e.g., a ventricularpump actuator) joined to make-up liquid supply conduits in several (orall) cells of a cell-stack.

FIG. 9 schematically illustrates a cell 900 that combines features ofFIG. 1 and FIG. 8 to form a cell in which one half-cell may begas-cooled, while the opposite half-cell is cooled by another mechanism(not shown). The negative half-cell 942 of FIG. 9 is configuredsimilarly to that shown in FIG. 8, comprising a hydrophobic membrane 923adjacent to the negative electrode 902 which abuts a separator membrane906 on an inner side. The negative half-cell 942 also comprises a gasinflow manifold 956, a gas-removal manifold 922, a gas-flow space 954joined to an electrolyte capture volume 910, and an electrolyte returnconduit 914.

The positive half-cell 932 of FIG. 9 comprises a positive electrode 904submerged in electrolyte 930 which may saturate a separator membrane 906between the positive 902 and negative 904 electrodes. The positivehalf-cell 932 may be joined to an electrolyte capture volume 912 and agas removal volume 988 by one or more fluid escape elements such as afluid egress channel 961 and/or a membrane 962. The electrolyte capturevolumes 910, 912 may be joined to corresponding electrolyte returnconduits 914, 916 through which electrolyte may be driven by one or morepumps 972, 974.

FIG. 10 represents embodiments of an electrochemical cell utilizingcertain features described herein. In some embodiments, FIG. 10represents embodiments of a gas-cooled PEM (proton exchange membrane)electrochemical cell, such as a low-flow PEM electrochemical cell,utilizing certain features described herein. In some embodiments, FIG.10 represents embodiments of a gas-cooled AEM (anion exchange membrane)electrochemical cell, such as a low-flow AEM electrochemical cell,utilizing certain features described herein. FIG. 10 schematicallyillustrates a cell 1000 with a separator membrane 1006 separating agas-side electrode 1002 from a liquid-side electrode 1004. In someembodiments, the separator membrane 1006 may be an ion-exchange membrane(i.e., a proton exchange membrane or an anion exchange membrane). Insome embodiments, the ion-exchange membrane may be liquid-impermeableand/or gas-impermeable. Optionally, any of the electrochemical cells,and any of the cell stacks, described in this application can includefeatures of cell 1000 according to FIG. 10 and as described here.

For the purpose of this description, the liquid-containing half-cell andits components will be referred to as “right-side” components and thegas-containing half-cell and its components will be referred to as“left-side” components, notwithstanding that actual implementations maytake many other positional configurations. If a proton exchange membrane(PEM) is used, the liquid-containing (right-side) half-cell may be thepositive-polarity half-cell. If an anion exchange membrane (AEM) isused, the liquid-containing (right-side) half-cell may be thenegative-polarity half cell.

The right-side half-cell chamber 1032 may be flooded with a liquid 1029which may be an electrolyte or a make-up liquid, such as but not limitedto process water. The liquid 1029 may saturate the separator or contactmembrane 1006, creating a three-phase solid-liquid-gas interface at orwithin the left-side electrode 1002. A phase-discriminating hydrophobicmembrane 1062 (or other fluid escape element) may separate theright-side half-cell chamber 1032 from a right-side gas-collectionvolume 1088 and right-side gas-removal manifold 1024. In the illustratedconfiguration, the right-side gas-removal manifold 1024 omits thegas-removal liquid described in connection with various embodimentsabove.

The cell of FIG. 10 may include a pressure-controlled gas-injectormanifold 1056 that directs a first gas into a left-side half-cellchamber 1042. The first gas injected into the left-side half-cellchamber may be identical to, a component of, or mixable with a gasproduced by the left-side electrode 1002 during electrochemicalreactions with the right-side counter-electrode 1004. The combinedinjected gas and gas produced at the left-side electrode may then becollected in a gas-removal manifold 1022.

The left-side gas-removal manifold 1022 of FIG. 10 also omits thegas-removal liquid described in connection with various embodimentsabove. In the embodiment of FIG. 10, the left-side half-cell chamber1042 is “liquid-free” or “gas-only.” Therefore, the gas mixture removedfrom the left-side half-cell chamber 1042 may be removed as gas alone.The gas-only state of the left-side half-cell chamber may be maintainedby controlling the gas pressure at the injection manifold 1056 to apressure sufficient to prevent the liquid 1029 from dripping into theleft-side half-cell chamber 1042.

Gas flowing through the left-side half-cell chamber 1042 mayadvantageously cool the cell 1000. For example, in embodiments in whichthe cell is a water electrolyzer producing hydrogen gas at the left-sideelectrode 1002 and oxygen at the right-side electrode 1004, the hydrogengas may flow through the left-side half-cell from a recirculationsystem, and may carry excess heat out of the cell. For example, in agas-cooled PEM configuration of FIG. 10, the negative half-cell chamber1042 (left-side) is “liquid-free” or “gas-only”. Therefore, the gas orgas mixture removed from the negative half-cell chamber 1042 may beremoved as gas alone. The gas-only state of the negative half-cellchamber may be maintained by controlling the gas pressure at theinjection manifold 1056 to a pressure sufficient to prevent the liquid1029 from dripping into the negative half-cell chamber 1042 through oraround the separator 1006. The gas pressure may be sufficient if it isapproximately equal to or greater than a liquid pressure in theliquid-filled half-cell chamber. In other embodiments, the gas pressuremay be sufficient if it is less than the liquid pressure in the positivehalf-cell by no more than the wetting pressure (or liquid ingresspressure or “bubble point”) of the separator membrane 1006. The wettingpressure of a membrane is an experimentally-determined property of amembrane (typically listed as a material property of some separatormembrane materials), defined as the liquid pressure difference from oneside of the membrane to the other at which the liquid penetrates themembrane and passes through to the opposite side.

In various embodiments, the configuration of FIG. 10 may be modified byreversing the polarity of the electrodes. Therefore, in suchembodiments, the positive (left-side) half-cell chamber 1032 would beliquid-free and the negative (right-side) half-cell chamber may beflooded with make-up liquid or electrolyte (right-side). For example, ina gas-cooled AEM configuration of FIG. 10, the negative half-cellchamber is filled with water or other make-up liquid 1029 and thepositive half-cell chamber may be cooled by flowing produced oxygen gasthrough the positive half-cell chamber. In some embodiments, the oxygengas in the positive half-cell chamber may be diluted by flowingsupplemental oxygen gas or another gas or gas mixture into and throughthe positive half-cell chamber. Such a dilution gas may be anon-reactive gas such as nitrogen, argon, or other substantiallynon-reactive gas or gas mixture.

In a cell-stack based on the system of FIG. 10, each cell in thecell-stack may include a right-side half-cell chamber 1032, a right-sideelectrode 1004, a left-side half-cell chamber 1042, a left-sideelectrode 1002, a fluid escape element 1062, and a separator 1006. Thesupply manifold 1078 and the gas-removal manifolds 1022, 1024 may bejoined to all other cells in the stack and to additional processingequipment, for example as described herein with reference to FIG. 4. Insome embodiments, fluid flow in the make-up liquid, such as but notlimited to process water, supply conduit may be driven by a single pumpactuator (e.g., a ventricular pump actuator) joined to make-up liquidsupply conduits in several (or all) cells of a cell-stack.

In various embodiments, features shown and described with reference toone of the figures may be combined with features shown and described ina separate figure, and such additional combinations are intended to bewithin the scope of this disclosure. For example, any of theconfigurations of FIG. 6-FIG. 9 may be modified to include a make-upliquid supply configuration as described with reference to FIG. 1 andFIG. 2.

Although various examples and embodiments provided above describeelectrochemical systems configured for electrolyzing water to producehydrogen and oxygen gases, the devices, systems, and methods describedherein may also be adapted and/or applied to various otherelectrochemical systems. In some embodiments, an electrochemical systemhaving features described herein may be an electrolyzer configured foruse in producing one or more chemicals.

One example is a chlor-alkali process in which an aqueous electrolytecontaining sodium-chloride is electrolyzed to produce chlorine gas andsodium hydroxide. In such examples, a make-up liquid may comprise asolution containing sodium chloride, and produced chemicals (e.g.,chlorine and sodium hydroxide) may be removed from each cell via aproduct-removal conduit (e.g., “a gas-removal manifold” as describedabove) in gaseous and/or liquid form.

In another example, an electrochemical system having features describedherein may be used to electrolyze a solution containing potassiumchloride to produce potassium hydroxide and chlorine gas. In such asystem, a supply manifold may deliver a make-up liquid comprising asolution containing potassium chloride, and produced chemicals (e.g.,chlorine and potassium hydroxide) may be removed from each cell via aproduct-removal conduit (e.g., “a gas-removal manifold” as describedabove) in gaseous and/or liquid form.

In other examples, electrochemical systems including devices, systems,and/or methods described herein may include electrowinning cells usedfor extracting metals from solutions containing the metal(s) asdissolved species. For example, some electrowinning cells may beconfigured for the production of zinc, platinum, gold, or other metals.In embodiments, such electrowinning systems may be configured to deliversolutions containing dissolved metals (e.g., an acidic or alkalineaqueous metal-containing solution) to be extracted as a make-up liquidvia a supply manifold.

In still further examples, electrochemical systems having devices,systems, and/or methods described herein may be adapted for performingelectrodialysis in which water is purified by the removal of ioniccontaminants under an applied electric field. Electrodialysis cellstypically include multiple chambers in fluidic series, each or some ofwhich may have features described herein.

Plate-And-Frame Cell-Stack Examples

Various features and components enabling confined electrolyteelectrolyzer systems are shown and described above schematically but maybe implemented in a plate-and-frame cell-stack made up of a plurality ofcell-frames incorporating electrolyte confinement, electrolytecapture-and-return, volume expansion, and other features as describedherein. FIG. 11-FIG. 13 illustrate some example plate-and-framecell-stack components embodying planar implementations of some of theconfined-electrolyte features described above. The electrolyteconfinement features, electrolyte capture-and-return features andsystems, expansion volume, and other features described with referenceto FIG. 11-FIG. 13 may be functionally similar to the features describedabove with reference to one or more of FIG. 1-FIG. 10.

Various example features of cell-frame structures will now be describedwith reference to FIG. 11-FIG. 12B. FIG. 11 is a perspective viewshowing a first assembled cell 1102 below and aligned with components ofa second cell 1104 shown in an exploded view. FIG. 12A illustrates afirst side 1202 of a cell-frame 1200 (a first half-cell chamber 1202partially filled with a visible compliant conductive layer 1112 and anelectrode 1114 behind the compliant layer 1112) while FIG. 12Billustrates the opposite side 1204 of the same cell-frame 1200 (a secondhalf-cell chamber 1204 partially filled with a visible compliantconductive layer 1122 and an electrode 1120 behind the compliant layer1122). Some features (or portions of features) are visible on only oneside of the cell-frame 1106, therefore in describing various features,reference may be made to a single figure or to all three figuressimultaneously. In various embodiments, the first half-cell may be thenegative half-cell and the second half-cell may be the positivehalf-cell. In other embodiments, the polarities of the illustratedhalf-cells may be reversed.

FIG. 11 shows some components of a complete cell 1104 in exploded viewwith a bipolar plate 1111 on top of a central assembly of components.Other features described herein are shown assembled in the cell-frame1106 for ease of description. The exploded components of the upper cell1104 include a bipolar plate 1110, a first compliant conductive layer1112, a first electrode 1114, a separator window 1116, a separatormembrane 1118, the cell-frame 1106 (containing various other componentsdescribed herein), a second electrode 1120, and a second compliantconductive layer 1122. When assembled, the various structures form arelatively thin cell assembly 1102. In some embodiments, the compliantconductive layers 1112, 1122 may be slightly deformed when compressed,thereby applying consistent compression forces across the surface of theelectrodes 1114, 1120, separators 1118, and bipolar plates 1110, 1111. Acompliant conductive layer 1112, 1122 may also beneficially provide anon-reactive region through which gas may escape each half-cell afterbeing generated on an electrode surface, therefore the compliantconductive layer may also be referred herein to as a “gas egress layer”.In other embodiments, a compliant conductive gas egress layer 1112, 1122may be omitted. A bipolar cell-stack may be formed by compressingmultiple cell assemblies 1102 between rigid end-plates (not shown).

FIG. 11-FIG. 13 illustrate planar cell-frame elements, each of whichcomprises electrochemical cell structures and electrolyte confinementstructures as described above. Although the features of FIG. 11-FIG. 12Bare shown implemented in circular disk-shaped structures, the same orsimilar features may be implemented in planar elements of any outershape, such as elliptical, oblong, square, rectangular, polygonal, etc.In some embodiments, a retention ring 1130 may surround one or morecell-frames 1106 so as to retain pressure within the interior of thecell-frame 1106. For example, in some embodiments, a cell-stack ofcell-frames 1106 may be operated at pressures of several to hundreds ofbar (i.e., hundreds of kPa to thousands of kPa) relative to a pressureoutside of the cell-frame perimeter. A retention ring 1130 may be madeof a metal, polymer, or composite material of sufficient tensilestrength to retain pressures within the cell-frame 1106 even if thecell-frame material itself is incapable of supporting such pressures.

In some embodiments, each cell-frame 1106 may contain featuressupporting a single electrochemical cell, including first and secondhalf-cell electrodes 1114, 1120 and chambers 1202, 1204 (filled by theelectrodes 1114, 1120 and compliant conductive layers 1112, 1122), anexpansion volume 1206 joined to both half-cell chambers 1202, 1204,gas-removal manifolds 1210, 1211 for both half-cells, a make-up liquidsupply manifold 1212 joined to a supply inlet 1214 supplying make-upliquid to at least one half-cell chamber 1202, and electrolytecapture-and-return systems for both half-cells. Alternatively, eachcell-frame may support features for half-cells of separate full-cells.That is, a full-cell may be formed by a first half-cell in a firstcell-frame and a second half-cell in a second adjacent cell-frame.

With reference to FIG. 11, a single cell-frame assembly 1202 maycomprise a cell-frame 1106, a positive electrode 1120, a separator 1118,a negative electrode 1120 and a bipolar plate 1110. A bipolar stack ofmultiple cells may be made by assembling multiple cell-frame assemblies1102 with one bipolar plate 1110, 1111 between each pair of adjacentcell-frames 1106. The cell-stack may be bolted or otherwise clampedbetween end-plates (not shown) to compress and seal the cell-frames 1106against one another. In various embodiments, each bipolar plate 1110,1111 may comprise the multi-layer bipolar plate described herein withreference to FIG. 15, or any other available single-layer or multi-layerstructures suitable as bipolar plates 1110.

In the example embodiment cell-frames shown in FIG. 11-FIG. 12B, a coversheet (not shown) may be used to seal various channels and volumes asfurther described below. For example, a cover sheet may be secured tothe cell-frame face shown in FIG. 12B in order to enclose variousstructures, manifolds, etc. O-rings, gaskets, or other structures mayalso be used to seal various conduits, manifolds, and other structuresagainst a cover-sheet or cell-frame of an adjacent cell-frame layer. Forease of illustration, the cover-sheet is not shown as it would otherwiseobscure described structures. Cover sheets may comprise one or morepieces of material as needed to seal various structures. Cover sheetsmay be secured to each cell-frame by adhesives (e.g., epoxies, solvents,silicones, etc.), welds (e.g., ultrasonic welds, laser welds, solventwelds, or others), compression, or other methods.

Suitable cover-sheet materials may comprise the same material (ormaterials) used in forming the cell-frame. Either or both the cell-frameand cover sheet may be made of polymers, metals, ceramics, or othermaterials resistant to degradation from electrolytes, including thevarious example materials listed elsewhere herein. For example, eitheror both the cell-frame and cover sheet may be made of: (i) metal ormetal alloys comprising nickel, titanium, aluminum, or any combinationsof these; (ii) polymer materials comprising nylon, polyethylene (PE),polypropylene (PP), polyolefins (PO), polyamide (PA),poly(tetrafluoroethylene) (PTFE), polyvinylidine fluoride (PVdF),poly(vinyl chloride) (PVC), polysulfone (PSU), polyphenylsulfone (PPSU),polyetheretherketone (PEEK), FEP (fluorinated ethylene propylene), PFA(perfluoroalkoxy), ETFE (ethylene tetrafluoroethylene), polyvinylalcohol or polyvinyl acetate (PVA), polycarbonates,polyvinylidenefluoride, polyacrylonitrile, polyetherimides, polyamide,cross-linked polyether, ethylene-methacrylic acid copolymers,fluorinated polymers, sulfonated polymers, carboxylic polymers, NAFION,or any combinations of these; (iii) asbestos, zirconium oxide cloth,cotton, ethyl-cellulose, methyl-cellulose, woven or non-woven cellulose,cellulose acetates, or any combinations of these; or (iv) anycombinations of any of these.

With reference to FIG. 12A and FIG. 12B, the electrolytecapture-and-return features are shown. A first half-cell chamber 1202 isformed on one side of the separator 1118 within the central region inwhich the compliant conductive layer 1112 is visible. The firsthalf-cell chamber is shown partially filled with a compliant conductivelayer and an electrode (not visible, behind the compliant conductivelayer). The second half-cell chamber is formed in the same manner on thesecond side of the cell-frame (as shown in FIG. 12B). The electrolyteconfinement and capture-and-return features associated with eachhalf-cell may be functionally substantially similar to one another withsome geometric variations. Therefore, while features associated withboth half-cells are shown in FIG. 12A and FIG. 12B, the followingdescription will generally be made with reference to features associatedwith one half-cell notwithstanding the fact that features associatedwith the opposite half-cell may be functionally substantially similarthose described. Each of egress channels 1220, headspace region 1222,drip chamber 1224, main gas separation chamber 1226, ventricular pump1234, electrolyte return channels 1252, 1254, 1256, gas-removal manifold1210, gas-purge manifold 1244, etc. can be independently present andassociated with the first half-cell as well as corresponding featuresassociated with the second half-cell. Alternatively, one or more ofthese or other features may be present and associated with only onehalf-cell, such structures being omitted for the second half-cell.

As shown in FIG. 12A, a first egress channels 1220 is shown extendingfrom a headspace region 1222 of the first half-cell chamber 1202 andhaving a second end in a drip-chamber 1224 of a two-chamber liquid-gasseparator. Liquid and gas transported by the egress channel 1220 fromthe first half-cell chamber 1202 to the first drip chamber 1224 may flowfrom the drip chamber 1224 to the main gas separation chamber 1226 by agas separator conduit 1225 (visible in FIG. 12B). An upper region of themain gas separation chamber 1226 forms a gas-collection volume 1258leading to a gas-removal manifold 1210 via a one-way valve in a gas exitport 1228 and a conduit 1229 (visible in FIG. 12B). In typicaloperation, a gas pocket may form in the gas-collection volume above aliquid-level in the main gas-separation chamber.

In some embodiments, the drip chamber 1224 and the main gas separationchamber 1226 may be substantially filled with metal foam or metal meshcondenser structures 1230, 1231, which may serve multiple purposes asdescribed below. The lower region of the main gas separation chamber1226 may comprise a hydrophilic element 1232 to collect liquidelectrolyte to be directed to an expansion volume 1206 or the firsthalf-cell chamber 1202 by a ventricular pump 1234 via an electrolyteremoval port 1246 and conduit 1248 (FIG. 12B). The expansion volume 1206may be joined to the first half-cell chamber 1202 and the secondhalf-cell chamber 1204 by conduits.

The egress channel 1220 for the first half-cell chamber 1202 (e.g., thenegative half-cell) is visible in FIG. 12A (partially obscured by asmall cover-sheet). A portion of the egress channel 1236 for the secondhalf-cell chamber 1204 (e.g., the positive half-cell) is visible in FIG.12B, while a portion passes through a hole in the cell-frame 1106 to thefirst side shown in FIG. 12A. As best seen in FIG. 12B, the egresschannels 1220, 1236 are shown as having an elongated stadium shape (arectangle with semi-circular ends). The egress channel of FIG. 12A andFIG. 12B is generally a long section of tubing wound multiple timesaround the stadium shape, creating a long pathway with curving andstraight sections through which gas and electrolyte may transit afterescaping a half-cell chamber 1202, 1204 before entering a drip chamber1224. As described above, the total path length, tortuosity,cross-sectional area, and material properties of an egress channel maybe varied in order to achieve a desired degree of pressure drop forliquid and gas passing through the egress channel.

In some embodiments, as shown in FIG. 12A and FIG. 12B, a filter 1238may be provided at an inlet end of an egress channel 1220, 1236 toprevent any small particles from clogging the egress channel 1220, 1236.If present, such a filter 1238 may be made of a porous material suitablyresistant to degradation by the electrolyte, for example metal orpolymer mesh, foam, or expanded material.

In the embodiment of FIG. 12A and FIG. 12B, the liquid-gas separatorsmay be divided into a drip chamber 1224 and a main gas separationchamber 1226. In some embodiments, both chambers 1224, 1226 may besubstantially filled by one or more porous condensers 1230, 1231. Thecondenser(s) 1230, 1231 may be made of a porous material (e.g., foam,mesh, or expanded material). The porous condenser material providessurfaces on which liquid electrolyte may condense, allowing the liquidelectrolyte to fall by gravity to a lower region of the drip chamber1224 and the main gas separation chamber 1226. Liquid electrolytecollecting at the bottom of the drip chamber may flow to the main gasseparation chamber 1226 by a conduit 1225 (FIG. 12B). Gas may alsofollow the same pathway 1225 but will tend to float as bubbles in theelectrolyte or as continuous gas channel in or above the liquidelectrolyte.

The condensers 1230, 1231 may also beneficially be made of a conductivematerial (e.g., a metal, carbon, graphite, or conductive polymer), whichmay allow for electronic detection of each “drip” of electrolyte exitingthe egress channel 1220 into the drip chamber 1224. This “dripdetection” operation may allow for continuous monitoring of the state ofoperation of each half-cell (and there for each full-cell) in acell-stack, as further described below. In various embodiments, thecondensers 1230, 1231 may be made of a single continuous piece ofmaterial or may comprise multiple pieces of material which may be indirect physical and/or electrical contact with one another via one ormore electrical conductors.

A lower region of the main gas separator chamber 1226 may comprise anelectrolyte-collection volume 1240 and electrolyte outlet 1246 (FIG.12B) for collecting electrolyte to be pumped back into the cell by aventricular pump 1235. The electrolyte-collection volume 1240 isfunctionally similar to the schematic structures for collectingelectrolyte described above with reference to FIG. 1 and FIG. 2. Theelectrolyte collection volume 1240 may comprise a hydrophilic structure1232 (partially visible through openings 1242 in the gas-separationcondenser 1231 in FIG. 12A), such as a section of separator membranematerial (as described herein), to substantially prevent or minimize gasegress through the one-way valve of the electrolyte outlet 1246.

As best seen in FIG. 12A, the condenser 1231 in the gas-separationchamber 1226 may comprise a plurality of relatively large-volume voids1242 in the otherwise porous material. Such voids 1242 may provideregions or pathways for gas to collect while liquid will tend tocondense on the surfaces of the porous condenser 1231 in regions betweenthe voids 1242. Gas may then collect in the upper-most region 1224 ofthe main gas-separation chamber 1226 adjacent to a gas outlet port 1228,which may comprise a one-way valve. As visible in FIG. 12B, the gasoutlet port 1228 may be joined to the gas-removal manifold 1210 by aconduit channel 1244 in the cell-frame 1106. The one-way valve in thegas outlet port 1228 may be generally configured to prevent back-flow ofgas or gas-removal liquid from the gas-removal manifold 1210 into themain gas-separation chamber 1226.

In some embodiments as shown, each half-cell may comprise a ventricularpump 1134, 1135 for pumping electrolyte from the electrolyte-collectionvolume 1240, 1241 of the gas-separation chamber 1226, 1227 into itsrespective half-cell chamber 1202, 1204 and/or into the expansion volume1206. As shown in FIG. 12B, the driven-fluid inlets 1246, 1247 of theventricular pumps 1134, 1135 may be located distant from the pumpchambers of the respective ventricular pumps 1234, 1235 and connected byconduits 1248, 1249 in the cell-frame 1106. Therefore, electrolytecaptured in the electrolyte-collection volumes 1240, 1241 of thegas-separation chambers 1226 may be drawn into the ventricular pump1234, 1235 and then driven by the ventricular pump into the pump outletport 1250, 1251 to the pump outlet flow channel 1252, 1253. The pumpoutlet flow channel 1252, 1253 may branch into a first conduit segment1254, 1255 leading to the half-cell from which electrolyte was collectedand a second conduit segment 1256, 1257 leading to the expansion-volume1206.

FIG. 12B shows example expansion channels 1255, 1257, 1254, 1256connecting each half-cell chamber 1202, 1204 to the expansion volume1206 via expansion volume ports 1286. The end 1158 of first half-cellexpansion channel 1254 visible in FIG. 12A may connect through a hole inthe cell-frame 1106 to the expansion channel 1254 visible in FIG. 12B.Similarly, a second half-cell expansion outlet 1289 visible in FIG. 12Bconnects to the end 1259 of expansion channel 1255 through two holesthrough the cell-frame 1106 covered by a cover sheet 1287 (FIG. 12A).

The expansion volume 1206 may be maintained at a pressure greater than asteady-state pressure of the half-cell chambers 1202, 1204 thereforecausing electrolyte to be preferentially driven from the ventricularpumps 1134, 1135 into the respective half-cell from which theelectrolyte was captured unless pressure in the half-cell chambers 1202,1204 is similar to or greater than pressure in the expansion volume1206.

As will be described further below with reference to FIG. 13, thepressure of the expansion volume 1206 may be controlled by a workingfluid delivered via a working fluid manifold 1320. In some embodiments,one or more working fluid purge manifolds 1288 (FIG. 12A and FIG. 12B)may extend through the cell-stack to facilitate purging or removingexcess working fluid from the working fluid side of the expansion volume1206.

In some embodiments, the cell-frames 1106 and cell-stack may compriseone or more gas-purge manifolds 1260, 1261 for each set of half-cells.The gas-purge manifolds 1260, 1261 may be used to purge any air or othergas remaining in each half-cell after assembly of the cell-stack andinitial introduction of electrolyte, make-up liquid, and/or workingfluid (as described further below). The gas-purge manifolds 1260, 1261may be joined to the drip chambers 1224, 1223 via one-way valves 1262,1263 arranged to allow fluid flow from the gas-purge manifolds 1260,1261 into the drip chambers 1224, 1223 (best seen in FIG. 12B).

A gas purge operation may be performed after initial assembly of thecell-stack or after re-assembly following some maintenance procedures. Agas-purge operation (described with reference to the first half-cell1202 but applicable to any half-cell in which a gas purge manifold ispresent) may comprise directing (e.g., pumping or otherwise driving) agas-purge liquid (e.g., make-up liquid, electrolyte, or a working fluidsuch as deionized water) into the gas-purge manifold 1260, through theone-way valve 1262, into the drip chamber 1224, and into thegas-separation chamber 1226. The ventricular pump 1234 may also beoperated during the gas-purge operation, driving the gas-purge liquidfrom the gas-separation chamber 1226 and into the half-cell chamber1202. As a result, any gases present in the half cell chamber 1202, thedrip chamber 1224 or the gas-separation chamber 1226 will ultimatelytend to be driven out of the cell-stack via the gas-removal manifold1210. In some embodiments, the gas-purge operation may be used toinitially fill each half-cell in the cell-stack with a desired volume ofelectrolyte. In other embodiments, electrolyte may already be present inthe half-cell chambers (and/or in one or more of the expansion volume1206, drip chamber 1224, and gas separation chamber 1226) prior toperforming the gas-purge operation.

As shown in FIG. 12A and FIG. 12B, the make-up liquid supply manifold1212 may be joined to an inlet port 1214 in the first half-cell chamber1202 by a conduit channel 1268 on the second side (FIG. 12B) of thecell-frame 1106. The inlet port 1214 may comprise a one-way valvearranged to allow make-up liquid to flow from the supply manifold 1212into the first half-cell chamber 1202 when pressure in the firsthalf-cell chamber 1202 drops below the controlled pressure in themake-up liquid supply manifold 1212. As described herein above, in otherembodiments a make-up liquid supply manifold may be configured todeliver make-up liquid to either one or both half-cell chambers 1202,1204.

In some embodiments, a cell-stack made up of cell-frames 1106 may beconfigured to electrically monitor portions of each half-cell. In theembodiments illustrated in FIG. 11-FIG. 12B, each cell-frame 1106 maycomprise electrical leads 1270, 1272, 1273 arranged to monitor electricpotentials between various components of the cell. In some embodiments,a bipolar plate lead 1270 may be electrically connected (e.g., by one ormore wires or other electrical conductors) to a bipolar plate 1110,1111. For example, in an embodiment best seen in FIG. 11, a tab 1176 maybe connected from a bipolar plate 1110, 1111 to an electrical contact onan adjacent cell-frame 1106. A first half-cell lead 1272 may beelectrically connected (e.g., by one or more wires or other electricalconductors) to the condenser(s) 1230, 1231 in the drip chamber 1224and/or the gas-separation chamber 1226 of the first half-cell.Similarly, a second half-cell lead 1273 may be electrically connected(e.g., by one or more wires or other electrical conductors) to thecondenser(s) 1277, 1275 in the drip chamber 1223 and/or thegas-separation chamber 1227 of the second half-cell.

An electrical potential (voltage) between the bipolar plate lead 1270and the first half-cell lead 1272 may be monitored for changes. Anelectrical circuit between the bipolar plate lead 1270 and the firsthalf-cell lead 1272 will be an open-circuit due to an electricaldiscontinuity in a physical gap 1278, 1279 between each egress channel1220, 1236 and the condenser 1230, 1277 in the respective drip chamber1224, 1223. The egress channel may be electrically conductive either bybeing made of or comprising a conductive material, and/or by virtue of aconductive electrolyte. The electrical circuit may be momentarily closedwhen a drop of electrically conductive electrolyte drips from an egresschannel 1220, 1236 onto the conductive condenser 1230, 1277 in the dripchamber 1224, 1223 thereby bridging the gap 1278, 1279 and closingelectrical discontinuity.

By monitoring the frequency, duration, voltage, and other aspects ofthese closed-circuit events (“drips”), various indicators of half-cellhealth or operation may be determined or estimated. By monitoring dripsin both half-cells, such indicators may be obtained for both half-cellsof each cell in a cell-stack. Therefore, in such embodiments, the “dripdetectors” in each half-cell (and therefore in each full cell) of acomplete cell-stack may be monitored individually to identify faults inindividual cells or half-cells.

For example, a continuously closed circuit (or a closed-circuit ofunusually long duration) in one half-cell's drip chamber may beindicative of an improperly functioning ventricular pump. Similarly,unusually long gaps between drips, or unusually high voltages mayindicate an improperly functioning electrode (or catalyst) or amalfunctioning egress channel. In another example, an unusually highvoltage between a half-cell lead 1272 or 1273 and a bipolar plate lead1270 may indicate a leak of working fluid into a half-cell chamber (asfurther described below). Many other metrics and indicators maysimilarly be deduced from signals or patterns obtained from theelectrical leads.

FIG. 13 illustrates “planar” expansion volumes 1300 a, 1300 b of twoadjacent cell-frames 1106 a, 1106 b in a cell-stack. In the illustratedexample, an expansion volume 1300 a, 1300 b may comprise a diaphragm1310 a, 1310 b separating an expansion volume side 1312 a, 1312 b (showncollapsed, i.e., zero percent expanded) from a “working fluid” side 1314a, 1314 b. The working fluid side 1314 a, 1314 b of the expansion volume1300 a, 1300 b may be filled with a working fluid via a working fluidmanifold 1320 (also visible in FIG. 12A and FIG. 12B) common to allcell-frames 1106 in a cell-stack. In various embodiments, the workingfluid may be any gas or liquid, such as deionized water, nitrogen,argon, etc. The working fluid may be maintained at a desired workingpressure, typically a pressure greater than a steady-state operatingpressure of the half-cell chambers of the cells. The working fluidpressure may be established, electromechanically controlled, andmaintained to exert a resistance to expansion of each expansion volume1300 a, 1300 b as described herein.

Working fluid may enter a working-fluid side of each expansion volume1300 a, 1300 b via the common working fluid manifold 1320 and through anopening 1325 a, 1325 b in a cover-sheet 1330 a, 1330 b secured to asecond-half-cell side of each cell-frame 1106. In some embodiments, theelectrolyte side 1312 a, 1312 b of each expansion volume 1300 a, 1300 bmay be defined by the diaphragm 1310 a, 1310 b, portions of thecell-frame 1106 a, 1106 b, and the cover sheet 1330 a, 1330 b. In otherembodiments, the electrolyte side 1312 a, 1312 b of each expansionvolume 1300 a, 1300 b may be defined only by the diaphragm 1310 a, 1310b, and the cell-frame 1106 a, 1106 b (in cases in which each cell-frameextends across the expansion volume.

Electrolyte and/or gas entering the electrolyte-side 1312 a, 1312 b ofeach expansion volume 1300 a, 1300 b via electrolyte entry ports (1286in FIG. 12B, not visible in the cross-section of FIG. 13) will tend toexpand the expansion volume 1300 a or 1300 b if the pressure of theelectrolyte and/or gas is greater than the established working fluidpressure. In some embodiments, the working fluid pressure may becontrolled at a different pressure during different stages of operationof the electrochemical system.

In some embodiments, a cell-frame 1106 may also comprise a coolantin-flow manifold 1292 and a coolant out-flow manifold 1294 configured todirect coolant into, through, and out of coolant channels in bipolarplate structures as described in some embodiments herein. In otherembodiments, coolant manifolds may be omitted or differently configured.In various embodiments, coolant may flow in either direction throughcoolant channels, therefore in some embodiment the coolant in-flow 1292and out-flow 1294 may be reversed.

Independent Thermal Management

In conventional electrolyzers, it is usually necessary to cool the cellsby circulating the electrolyte through them, and the electrolyte exitingfrom the cell carries with it the gas produced. In many designs,separation of the gas from the electrolyte is accomplished in aseparating drum external to the electrolyzer. The electrolyte, free ofgas, is then re-circulated through the cells. In the various confinedelectrolyte systems described herein, separation of gas and electrolyteis performed within each cell-frame, and electrolyte is not pumped outof the cells. In such systems, a separate mechanism for removing heatfrom the cell-stack may be beneficial.

The embodiments of systems and methods described in this section, suchas embodiments associated with thermal management in electrochemicalsystems, such as electrolyzers, optionally can be combined with otherembodiments of systems and methods described elsewhere in thisapplication. For example, any of the confined electrolyteelectrochemical cells described throughout this application can includeor be used with any of various embodiments described in this section,such as thermal management components.

FIG. 14A and FIG. 14B illustrate example embodiments of electrolyzersystems 1400, 1401 with thermal management components independent ofprocess water components. The coolant loop 1430 in FIG. 14A is shownsubstantially the same as the coolant loop 1431 in FIG. 14B.

In various embodiments, the coolant loop 1430, 1431 may comprise a pumpconfigured and arranged to drive a cooling fluid through coolantconduits and one or more heat exchangers 1432 inside the stack 1410 aswell as one or more heat-expelling heat exchangers 1434 outside of thestack 1410. In some embodiments, as shown for example in FIG. 14A, thestack heat exchangers may comprise bipolar plate structures 1416configured with coolant conduits 1432 to cool a bipolar stack 1410 atthe interface between adjacent cells 1415 (and/or at the ends of thestack 1410). In other embodiments, a heat exchanger in the stack 1410may be configured to remove heat from edges of each electrochemical cell1410 in the stack instead of or in addition to removal of heat viabipolar plate coolant conduits 1432.

FIG. 14A illustrates an example electrolyzer system 1400 comprising acell-stack 1410 in a bipolar configuration. Each cell 1415 comprises afirst electrode 1412 in a first half-cell chamber 1422 and a secondelectrode 1414 in a second half-cell chamber 1424. The polarity of thefirst electrode 1412 and second electrode 1414 may depend on the type ofion exchange membrane or other factors as described herein. Bipolarplates 1416 between adjacent cells 1415 may contain coolant conduits1432. A coolant circulation pump 1436 may be configured to circulate acoolant fluid through the bipolar plates 1432, through an externalheat-exchanger 1434, and return the coolant to the bipolar plates 1416.Separately, a process water circulation pump 1452 may be configured tosupply process water to each cell 1415 via the supply manifold 1440, andto direct process water to gas-collection manifolds 1442, 1444 which mayremove produced gases from the cells as further described below.

In alternative electrolyzer systems, coolant conduits may be arranged tosurround or run adjacent to an exterior of each cell 1415 of thecell-stack 1410 rather than through bipolar plates 1416. In suchembodiments, heat may be conducted in the electrodes, and collected bycoolant fluid in the coolant conduits at a periphery of the cell. As inprevious embodiments, a coolant circulation system may be configured tocirculate coolant between the coolant conduits and an externalheat-exchanger. In some embodiments, such coolant conduits may beintegrated into one or more cell and/or stack frame structures or otherstructures in a cell-stack.

The cooling fluid may be any liquid or gas suitable for carrying heatout of the cell-stack. In various embodiments, the cooling fluid may bea liquid such as water (including deionized water or less-pure water), aglycol (e.g., ethylene glycol and/or propylene glycol), a dielectricfluid (e.g., perfluorinated carbons, polyalphaolefins, or oils), or agas such as air, hydrogen, oxygen, nitrogen, argon, any combination ofthese, etc.

Thermal Management: Bipolar Plate Heat Exchanger

FIG. 15 provides a schematic exploded view illustration of a multi-layercooling bipolar plate 1500 with a coolant conduit 1510 through whichcoolant may be circulated. In the illustrated example, the bipolar plate1500 comprises three layers 1522, 1524, 1526 of conductive material. Achannel layer 1526 may be sandwiched between two outer layers 1522,1524. The channel layer 1526 may comprise one or more flow channels 1510arranged to direct coolant through the space between the outer layers1522, 1524. In some embodiments, the flow channel(s) 1510 may bearranged in a pattern chosen to minimize conductive paths to all partsof an electrode contacting one of the outer layers 1522, 1524. In otherembodiments, flow channels 1510 may be arranged to optimize a flow rateor other characteristics of coolant flow through the channels 1510.

The three layers 1522, 1524, 1526 may be sealed and secured by welds(e.g., laser-welds, sonic welds, resistance welds, or other weldtechniques) around at least the perimeter of the plates 1522, 1524,1526, leaving at least an in-flow port 1532 and an out-flow port 1534.Alternatively, the layers 1522, 1524, 1526 may be sealed and/or securedby other techniques or materials such as adhesives, O-rings, or othermethods as desired.

At least the outer layers 1522, 1524, 1526 may be made of a materialcompatible with the high-purity process water and/or the coolant fluidto be directed through the channels 1510. For example, some or all ofthe layers may be made of nickel or other conductive material (e.g.,steel) that is coated, plated, or otherwise covered with nickel or otherconductive material that is non-reactive in the electrolyzerenvironment.

In alternative embodiments, a cooling bipolar plate 1500 may be madefrom only two layers, one or both of which is machined, stamped orotherwise modified to produce one or more flow channels between thelayers.

Exemplary Ion Exchange Membrane Configurations: Low-Flow Ion-ExchangeElectrolyzers

De-coupling the function of cooling a cell-stack from the function ofsupplying water to be split, one can realize substantial cost savings byeliminating high-cost plant components required by circulating andcooling process water. Various methods, systems, and components forachieving such decoupling are described herein. In some embodiments,this decoupling may be achieved by using a second, separate coolantfluid to remove heat from a cell/stack while introducing process waterto the cell/stack at a rate that is not substantially greater than arate of water consumption. Such a system will be referred to herein as a“low-flow ion-exchange” (or “LFIE”) electrolyzer.

Embodiments of LFIE electrolyzer systems may also benefit from inclusionof various features or elements of electrolyzer systems describedthroughout this application. For example, an LFIE electrolyzer maycomprise a make-up liquid supply system, fluid escape elements,gas-removal manifolds or channels, and/or expansion chambers. Each ofthese elements may comprise structures and methods described throughoutthis application. In further embodiments, any other compatiblestructures or methods described throughout this application may beincorporated into one or more LFIE electrolyzer as described herein. Forexample, in some embodiments, a fluid escape element in an LFIEelectrolyzer may be configured to impart minimal or zero flow resistanceto liquid or gas escaping each half-cell. In such embodiments, a fluidexit channel may be substantially open and unrestricted. In someembodiments, a fluid exit channel may comprise a “waterfall” arranged torequire a particular volume of water to overcome a level before waterexits a half-cell chamber. In such an arrangement, gas may exit thehalf-cell freely, and water will only exit at a rate at which it exceedsthe waterfall level. Therefore, in such embodiments, a water exit ratewill be equal to the positive difference between a water supply rate anda water consumption rate. In an LFIE electrolyzer with a waterfall fluidexit, a water flow rate through the cells may be controlled by supplyingwater at a rate that exceeds an expected consumption rate by a desiredflow rate (or replacement rate) as described herein.

In some embodiments, an LFIE electrolyzer may comprise a make-up liquidsupply system and other elements arranged to supply make-up liquidconsisting essentially of deionized water into the cells at a rate onlyslightly greater than a rate at which water is consumed by splittinginto constituent gases. Coupled with a separate thermal managementsystem, such an LFIE electrolyzer system may be made and operated at amuch lower cost when compared to conventional ion-exchangeelectrolyzers.

FIG. 14A and FIG. 14B schematically illustrate high-level systemdiagrams showing example flows of process water and coolant through acell-stack 1410. The LFIE electrolyzer systems 1400, 1401 of FIG. 14Aand FIG. 14B each comprise a cell-stack 1410 made up of a plurality ofelectrochemical cells 1415, each cell having a first half-cell 1422 anda second half-cell 1424 separated by respective ion-exchange membranes1418. As described in further detail below, depending on the type ofion-exchange membrane used, process-water, and/or another electrolyte ormake-up liquid, may be supplied to a positive half-cell or a negativehalf-cell. The half-cells 1422, 1424 will be described generically herewithout reference to polarity but will be further described below in thecontext of PEM and AEM separator membranes with reference to electricalpolarity.

The systems 1400, 1401 each comprise a coolant loop 1430, 1431 with apump 1436 configured to direct a coolant fluid through in-cell heatexchangers 1432 to remove heat from the cell-stack 1410 and through anexternal heat exchanger 1434 to reject heat from the coolant fluid to alower-temperature heat sink. Notably, the coolant loop 1430, 1431 isindependent of process water supply 1436 and return 1438 conduits.Further details of independent thermal management systems useful inelectrochemical systems such as LFIE electrolyzers are described infurther detail above and throughout this application.

FIG. 14A illustrates a process water supply manifold 1440 arranged todirect process water into a first half-cell 1422 of each cell 1415.Process water may then be split in each cell, and produced gases may becollected in first 1442 and second 1444 gas removal manifolds. A smallvolume of excess process water may exit each cell along with gasproduced in the first half-cell 1422. The small quantity of excess waterexiting the cell-stack 1410 may be separated from the collected gas at aliquid-gas separator 1450. The collected gas may be further treated(e.g., dried, cooled, etc.), and excess water may be returned by a pump1452 to the process water supply manifold 1440 along with water from amake-up water reservoir 1454.

FIG. 14B illustrates a process water supply manifold 1440 arranged todirect process water into a first half-cell 1422 of each cell 1415 whilealso flowing a portion of process water through a first gas collectionmanifold 1442. In the system of FIG. 14B, gas produced in the firsthalf-cell may be collected in a water stream, thereby allowing thecollected gas to be cooled by the process water. The combined water/gasflow may be separated at a liquid-gas separator 1450, and excess watermay be returned by a pump 1452 to the process water supply manifold 1440along with water from a make-up water reservoir 1454.

The process water loop 1461 shown in FIG. 14B may also include a stackbypass conduit 1456 through which a quantity of process water may flowafter leaving the supply manifold 1440 so as to maintain a liquid volumein the first gas removal manifold 1442, the fluid pressure of which maybe regulated at a pressure regulator 1462.

The bypass conduit 1456 in the process water loop 1461 of FIG. 14B isomitted in the process water loop 1460 shown in FIG. 14A. As a result,the only path for process water from the supply manifold to theliquid-gas separator 1450 is through the first half-cells 1422 of thecell stack 1410. Therefore, in the arrangement of FIG. 14A, the flowrate of process water through the process water loop 1460 is limited bythe flow rate of water exiting the first half-cells 122.

Notably, each of the systems according to FIG. 14A and FIG. 14B can beconfigured as a PEM system, by applying a positive polarity to the firsthalf-cells 1422, or as an AEM system, by applying a negative polarity tothe first half-cells 1422 into which process water is supplied, as alsodescribed throughout in this application.

Exemplary Ion Exchange Membrane Configurations: LF-PEM CellConfigurations

FIG. 16 schematically illustrates components of an electrochemical cell1600 in a low-flow PEM electrolyzer. The cell 1600 may include apositive half-cell chamber 1602 filled with process water 1606 (e.g.,deionized water to be split in the electrolyzer) supplied via a supplymanifold 1610. A positive electrode 1612 comprising an oxygen-evolutioncatalyst may be positioned within the positive half-cell chamber 1602and submerged in the process water 1606. A proton exchange membrane(PEM) separator 1620 may separate the positive half-cell chamber 1602from a negative half-cell chamber 1604 and may be in contact with anegative electrode 1614 and the positive electrode 1612. The negativeelectrode 1614 may comprise a hydrogen-evolution catalyst. Variousexample positive and negative catalyst materials are describedthroughout this application. In a typical PEM configuration, thenegative half-cell chamber 1604 may be substantially gas-filled as thePEM separator 1620 may prevent water from entering the negativehalf-cell chamber 1604 under normal conditions.

During operation, the process water 1606 is electrochemically split inthe positive half-cell chamber 1602 to produce oxygen gas in thepositive half-cell chamber 1602. The oxygen gas produced at the positiveelectrode 1612 may be withdrawn from the positive half-cell chamber 1602via a positive gas-removal manifold 1630. In some embodiments, amixed-flow of oxygen gas and excess process water may exit the positivehalf cell chamber 1602 via a common fluid escape element 1636 arrangedbetween the positive half-cell chamber 1602 and the positive gas-removalmanifold 1630. The fluid escape element 1636 may comprise any fluidescape element structure as described throughout this application,including “egress channels” or hydrophobic membranes as describedtherein.

Hydrogen atoms (protons) from the water-splitting reaction may be drivenacross the PEM separator 1620 towards the negative electrode 1614 atwhich they will be electrochemically combined to form hydrogen gas. Thehydrogen gas may be withdrawn from the negative half-cell chamber 1604via a negative gas-removal manifold 1640 In some embodiments, thenegative gas-removal manifold 1640 may be regulated at a desiredpressure by a pressure regulator 1642. In various embodiments, thepressure regulator 1642 may be operated to maintain the negativegas-removal manifold 1640 at a pressure of up to 50 bar or more. Forexample, the negative gas-removal manifold pressure may be regulated at20, 30, 40, 50, 60, 70, 80, 90, or 100 bar.

In various embodiments, pressure in the positive gas removal manifold1630 may be regulated by a pressure regulator 1644 to be slightly lowerthan a fluid pressure in the supply manifold 1610 which may be regulatedby a pressure regulator 1646. In various embodiments, the pressureregulator 1644 may be configured to maintain fluid (a gas-removal liquidand/or a gas only) in the negative gas-removal manifold at a pressure ofat least 10 bar, up to 30 bar, 40 bar, 50 bar, 60 bar, 70 bar, 80 bar,90 bar, 100 bar, or more.

In some embodiments, each positive half-cell of a low-flow PEMelectrolyzer stack may comprise a liquid-gas separator (e.g., as shownin FIG. 1 or FIG. 11-FIG. 12B) to capture and separate gas from liquidwater escaping from the positive half-cell via a fluid escape element1636. Captured liquid water may be returned to the positive half-cell byconduits and a pump (e.g., a ventricular pump) unique to the cell (e.g.,as shown in FIG. 3A-FIG. 3C, among others). Alternatively, liquid-gasseparation and water return may be performed on a stack-level or on asystem level as described herein with reference to FIG. 14A and FIG.14B.

As shown in FIG. 16, some embodiments of a low-flow PEM electrolyzer mayalso include an expansion chamber 1650 joined in fluid communicationwith the positive half-cell chamber 1602. As described throughout thisapplication, an expansion chamber 1650 may be configured to allowvolumetric expansion of a liquid/gas mixture in a half-cell chamber 1602while maintaining fluid pressure within a desired range. In variousembodiments of a low-flow PEM electrolyzer, an expansion chamber 1650may be positioned in fluid communication with one or both half-cellchambers as needed. An expansion chamber 1650 may be configured toimpart a resistance to expansion, requiring increasing pressure tofurther expand the volume. Alternatively, an expansion volume may beconfigured to allow substantially unrestricted volumetric expansion upto a volumetric limit.

With reference to FIG. 14A and FIG. 14B, a low-flow PEM electrolyzersystem may comprise two independent fluid circulation loops: a processwater loop 1460, 1461 and a coolant loop 1430, 1431. The process waterloop 1460, 1461 may be configured to deliver fresh process water to thepositive half-cells (the first half-cells 1422 having a positivepolarity in this case) of the cell stack 1410. A mixture of excessprocess water and oxygen gas may be withdrawn from outlets of the firsthalf-cells 1422 of the cell-stack 1410. The oxygen gas may be separatedfrom the excess process water in a liquid/gas separator 1450, and theexcess process water may be returned to the cell-stack 1410 along withadditional water from a make-up water source 1454 (e.g., a waterde-ionizing system supplied by a municipal water source or other waterreservoir).

In some embodiments, the process water loop 1460, 1461 may comprise apump 1452 to drive both excess process water from the liquid/gasseparator 1450 and from the make-up water supply 1454. The pump 1452and/or a pressure regulator 1464 located downstream of the supplymanifold 1440 may be used to control a pressure of the process watersupplied to the cell-stack 1410. A separate pressure regulator 1466located downstream of the first gas collection manifold 1442 may beconfigured to control a pressure in the gas-collection manifold 1442 atthe outlet of the cell-stack 1410. Each of the pressure regulators 1462,1464 may be any type of pressure regulator available and suitable to theapplication, such as a back-pressure regulating valve, or others.

Hydrogen gas may be collected in the conduits and gas removal manifold1444 exiting the second half-cells 1424 of the cell-stack 1410. In someembodiments, fluid pressure in the second gas removal manifold 1444 maybe regulated by a pressure regulator 1466 located downstream of thesecond gas removal manifold 1444. The hydrogen gas may be directed to agas collection system 1470 configured to treat (e.g., purify, dry,compress, cool, etc.) and store or use the hydrogen produced by thestack 1410. In some embodiments, the gas collection system 1470 may alsocomprise additional gas treatment components, such as heat exchangers,compressors, dryers, etc.

The process water loop 1460, 1461 may generally be configured tocirculate process water at a very slow flow rate (e.g., read below) whencompared to PEM and AEM electrolyzer systems in which process water isused for cooling. For example, in a low-flow electrolyzer, water may bepumped (or otherwise driven) into the PEM cell-stack at flow rateshundreds or thousands of times lower than process water-cooled systems.In an LFIE electrolyzer process water need only be supplied to theelectrochemical cell-stack at a rate sufficient to replace waterconsumed and to maintain wetting of cell components sufficient tomaintain an effective three-phase interface (or triple point).

Typical PEM water electrolyzers of megawatt scale may operate withprocess water flow rates of hundreds of gallons per minute per celldespite consuming water at rates approaching less than a gallon perminute per cell. In other words, an ion-exchange membrane electrolyzerutilizing process water for cooling requires process water flow rateshundreds of times greater than the rate at which process water isconsumed by splitting. Such high flow rates are required in order toadequately remove heat via the process water. By using a separatecoolant fluid independent of the process water, such high flow rates maybe avoided.

By contrast, process water flow rates into an LFIE electrolyzer mayideally be roughly equal to a rate at which process water is consumedvia splitting. In some cases, it may be beneficial to drive processwater flow rates slightly greater than a rate of consumption in order tomaintain wetting of cell components, to account for differences inconsumption rates between cells and ensure that all cells in a stack arereceiving water at least as fast as it is consumed, or for otherreasons. The flow rate can be controllable such that the flow ratematches or exceeds the consumption rate so that the electrode poresremain wetted with enough water to continue efficiently splitting.

The rate of gas production by water splitting is generally a functionwater temperature, pressure, and applied electrical current, each ofwhich may be a controlled parameter within an electrolyzer system, andtherefore a rate of water consumption by each cell of a cell-stack maybe at least approximately known based on at least these controllablefactors. Therefore, in various embodiments, process water may bedelivered into an LFIE cell at a rate defined as a percentage relativeto a water consumption rate. For example, process water may be deliveredat a rate of between about 0.01% and about 400% greater than aconsumption rate (i.e., at a rate of about 100.01% to about 500% of theconsumption rate). In some particular embodiments, a rate of processwater delivery may beneficially be between about 101% and about 150% ofthe expected consumption rate. In specific embodiments, water may besupplied at rates of about 100.01%, 100.05%, 100.1%, 100.5%, 101%, 105%,110%, 125%, 150%, 175%, 200%, 300%, 400%, or 500% of the expected waterconsumption rate. In other embodiments, higher process water deliveryflow rates may be used (e.g., as high as 100 times a consumption rate or1000% of the consumption rate), while still remaining substantiallylower than flow rates required when using process water as the soleheat-transfer fluid. Therefore, in some embodiments, a low-flowion-exchange electrolyzer may utilize a process water supply rate of nomore than 1,000% of a rate at which the water is consumed.

In some embodiments, a flow rate of process water flowing into an LFIEelectrolyzer may be defined and/or controlled based on a rate at whichthe process water is consumed by water-splitting reactions. For example,a flow rate of process water may be controlled as a function of appliedelectrical current, as a function of a gas collection rate, or othermeasurable variables related to a water consumption rate.

In various embodiments, such flow rates may be controlled based on arate of process water delivery to the cell-stack. For example,flow-based control may be accomplished by a closed-loop controllerconfigured to control a water delivery flow rate based on feedback of ameasurement of a mass flow rate or a volumetric flow rate into thecell-stack. Alternatively or in addition, process water flow rates maybe based on a pressure of process water in a process water supplymanifold delivering water to the cell-stack. For example, pressure-basedcontrol may be performed by a closed-loop controller configured tomaintain a fluid pressure in a supply manifold based on feedback fromone or more pressure sensors. Alternatively, flow-based orpressure-based control may comprise an open-loop control system withoutfeedback measurements. Some examples of pressure-based flow controlsystems and methods are described below.

At such low replacement rates, the volume of liquid water flowingthrough the oxygen-containing second gas removal manifold 1444 andassociated conduits exiting the cell-stack will be very small. As aresult, a liquid-gas separator 1450 may be very small and simple. Forexample, the liquid-gas separator 1450 may simply comprise a verticalT-connected conduit with a vertical leg flowing upwards to carry awaygas and a vertical leg flowing downwards to collect liquid water. Insome embodiments, a liquid-gas separator may also comprise a dryer suchas a desiccant bed or a water vapor condenser to remove water vapor fromthe flowing gas.

Exemplary Ion Exchange Membrane Configurations: LF-AEM CellConfigurations

FIG. 17 schematically illustrates components of an electrochemical cell1700 in a low-flow AEM electrolyzer. As shown, a low-flow AEMelectrolyzer system may be substantially similar to a cell 1600 in alow-flow PEM electrolyzer system with the main difference being theintroduction of process water 1708 into the negative half-cell chamber1704 in the AEM case rather than into the positive half-cell chamber1602 in the PEM case.

As shown in FIG. 17, the cell 1700 may include a negative half-cellchamber 1704 filled with process water 1708 (e.g., deionized water to besplit in the electrolyzer) supplied via a supply manifold 1710. Anegative electrode 1714 comprising a hydrogen-evolution catalyst may bepositioned within the negative half-cell chamber 1704 and submerged inthe process water 1708. An anion exchange membrane (AEM) separator 1720may separate the negative half-cell chamber 1704 from a positivehalf-cell chamber 1702 and may be in contact with the negative electrode1714 and a positive electrode 1712. The positive electrode 1712 maycomprise an oxygen-evolution catalyst. The positive half-cell chamber1702 may be substantially filled with a produced gas (e.g., oxygen) asthe AEM separator 1720 may prevent water from entering the positivehalf-cell chamber 1702 under normal conditions.

During operation, the process water 1708 is electrochemically split inthe negative half-cell chamber 1704 to produce hydrogen gas in thenegative half-cell chamber 1704. The hydrogen gas produced at thenegative electrode 1714 may be withdrawn from the negative half-cell1704 via a negative gas-removal manifold 1740. In some embodiments, amixed-flow of hydrogen gas and excess process water may exit thenegative half-cell chamber 1704 via a fluid escape element 1736 arrangedbetween the negative half-cell chamber 1704 and the negative gas-removalmanifold 1740. Example structures and configurations useful as fluidescape elements are described herein throughout, any of which may beused in a cell as illustrated in FIG. 17.

Oxygen atoms from the water-splitting reaction will tend to cross theAEM separator 1720 toward the positive electrode 1712 at which oxygengas is formed. The oxygen gas may be withdrawn from the positivehalf-cell chamber via a positive gas-removal manifold 1730.

In order to produce generated hydrogen gas at high pressure, the processwater may be injected at an absolute pressure slightly higher than thedesired hydrogen gas pressure. In some embodiments, a pressure regulator1746 may be used to regulate pressure of the process water supplied tothe negative half-cell chamber 1704 via a supply manifold 1710. In someembodiments, water in the process water supply manifold 1710 may bemaintained at a high pressure so as to maintain a high fluid pressure inthe negative half-cell chamber 1704, thereby producing hydrogen gas andoxygen gas at high pressure. For example, in some embodiments, it may bedesirable to collect produced hydrogen (and/or oxygen) at pressures of30 bar or more, or as high as 100 bar or more in some cases. In suchembodiments, process water may be supplied at pressures from atmosphericpressure up to 100 bar or more, such as about 1 bar, 10 bar, 20 bar, 30bar, 40 bar, 50 bar, 60 bar, 70 bar, 80 bar, 90 bar, 100 bar, or more.Gas produced by splitting water at such pressures may be collected atpressures only slightly lower than the process water pressure, such as0.5 bar.

In some embodiments, the negative gas-removal manifold 1740 may beregulated at a desired pressure by a pressure regulator 1742. In variousembodiments, the pressure regulator 1742 may be operated to maintain thenegative gas-removal manifold 1740 at a pressure slightly lower than apressure in the supply manifold 1710 regulated by the pressure regulator1746 at which the process water is supplied to the negative half-cellchamber 1704.

In some embodiments, oxygen removed from the positive half-cell 1702 maybe maintained at a desired pressure by a pressure regulator 1744 in thepositive gas-removal manifold 1730. In various embodiments, the pressureregulator 1744 may be configured to maintain fluid (a gas-removal liquidand/or a gas only) in the positive gas-removal manifold at a pressure ofat least 10 bar, up to 30 bar, 40 bar, 50 bar, 60 bar, 70 bar, 80 bar,90 bar, 100 bar, or more.

In some embodiments, each negative half-cell of a low-flow AEMelectrolyzer stack may comprise a liquid-gas separator (e.g., as shownin FIG. 1 or FIG. 11-FIG. 12B) to capture and separate produced gas fromliquid water escaping from the negative half-cell via a fluid escapeelement 1736. Captured liquid water may be returned to the negativehalf-cell by conduits and a pump (e.g., a ventricular pump) unique tothe cell (e.g., as shown in FIG. 3A-FIG. 3C, among others).Alternatively, liquid-gas separation and water return may be performedon a stack-level or on a system level as described herein with referenceto FIG. 14A and FIG. 14B.

As shown in FIG. 17, some embodiments of a low-flow AEM electrolyzer mayalso include an expansion chamber 1750 joined in fluid communicationwith the negative half-cell chamber 1704. As described hereinthroughout, an expansion chamber 1750 may be configured to allowvolumetric expansion of a liquid/gas mixture in a half-cell chamber 1704while maintaining fluid pressure within a desired range. Variousexamples and embodiments of volume expansion systems are describedherein below.

With reference to FIG. 14A and FIG. 14B, a low-flow AEM electrolyzersystem may comprise two independent fluid circulation loops: a processwater loop 1460, 1461 and a coolant loop 1430, 1431. The process waterloop 1460, 1461 may be configured to deliver fresh process water to thenegative half-cells (the first half-cells 1422 having a negativepolarity in this case) of the cell stack 1410. A mixture of excessprocess water and hydrogen gas may be withdrawn from outlets of thefirst half-cells 1422 of the cell-stack 1410. The hydrogen gas may beseparated from the excess process water in a liquid/gas separator 1450,and the excess process water may be returned to the cell-stack 1410along with additional water from a make-up water source 1454 (e.g., awater de-ionizing system supplied by a municipal water source or otherwater reservoir).

In some embodiments, the process water loop 1460, 1461 may comprise apump 1452 to drive both excess process water from the liquid/gasseparator 1450 and from the make-up water supply 1454. The pump 1452and/or a first pressure regulator 1464 may be used to control a pressureof the process water supplied to the cell-stack 1410. A second pressureregulator 162 may be configured to control a pressure in the firstgas-collection manifold 1442 at the outlet of the cell-stack 1410. Insome embodiments, a pressure regulator 1466 may be used to regulatepressure in the second gas removal manifold 1444. Each of the pressureregulators 1462, 1464, 1466 may be any type of pressure regulatoravailable and suitable to the application, such as a back-pressureregulating valve, or others.

Oxygen gas may be collected in the second gas removal manifold 1444 andassociated conduits exiting the second half-cells 1424 of the cell-stack1410. The oxygen gas may be directed to a gas collection system 1470configured to treat (e.g., purify, dry, compress, cool, etc.) and store,use, or vent the oxygen produced by the stack 1410. In some embodiments,the gas collection system 1470 may also comprise additional gastreatment components, such as heat exchangers, compressors, dryers, etc.

In some embodiments, the excess oxygen gas withdrawn from the cell-stackmay be at a high pressure slightly lower than a pressure of the processwater in the negative half-cell chamber 1422. In such embodiments, thehigh-pressure oxygen gas may be utilized to pre-pressurize process waterdrawn from the make-up water source 1454. For example, a fluidpressure-exchange device (not shown) may be used to transfer the highpressure of the oxygen gas to the make-up water 1454 to be delivered tothe cell-stack 1410. Examples of suitable fluid pressure-exchangers mayinclude those taught by U.S. Pat. No. 7,306,437 and references therein.In other embodiments, the oxygen gas collected from the cell-stack maybe at or near atmospheric pressure, and may simply be vented to theatmosphere if not needed for other purposes.

The process water loop may generally be configured to circulate processwater at a relatively slow flow rate. For example, water may be pumped(or otherwise driven) into the AEM cell-stack 1410 at the same flowrates or replacement rates described above with respect to PEM systems.While process water in an AEM system may be delivered at a higherabsolute pressure, the relative pressures and flow rates may be withinthe same ranges and values as described above.

In various embodiments, process water may be delivered to the cell-stack1410 and distributed to each cell 1415 at a relatively “low” flow rateas described above. In some embodiments, supply of process water may beachieved by controlling fluid pressure in a water supply conduit ormanifold as described herein throughout with reference to make-up liquidsupply structures and methods. In various embodiments of a low-flowion-exchange electrolyzer, a process water supply inlet may comprise oneor more one-way valves arranged to deliver a bolus of water to a cell(or a cell-stack) when a pressure difference across the valve exceeds apre-determined cracking pressure, thereby causing intermittent deliveryof water to the cell or stack. In other embodiments, a one-way valve1660 FIG. 16 or 1760 in FIG. 17 at a water inlet may be omitted, andwater may be free to flow bidirectionally through the inlet between thesupply manifold and the half-cell chamber.

Some embodiments of LFIE electrolyzers may be configured to deliverprocess water to both half-cell chambers 1802, 1804, as schematicallyillustrated in FIG. 18. Such a system may comprise either PEM or AEMseparators, and may be operated at atmospheric or higher pressures. Thesystem of FIG. 18 includes: half-cell chambers 1802, 1804; a PEM or AEMseparator membrane 1820; gas removal manifolds 1840, 1843; fluid escapeelements 1835, 1836; expansion chamber 1850; and liquid electrolyte1806, 1807. As described above, electrochemical splitting of water willtend to happen preferentially in one half-cell depending on the natureof the ion-exchange membrane in use. As a result, a water consumptionrate in one half-cell may be substantially lower (or even zero) relativeto the consumption rate in the other half-cell. In variousimplementations, water in a half-cell with a low consumption rate may beheld static (e.g., by a phase-discriminating fluid escape membraneallowing only gas to pass through), or may be removed at a slow ratealong with produced gas.

Electronic Controllers

Referring next to FIG. 19, shown is a block diagram depicting physicalcomponents of an electronic controller that may be utilized to realizeone or more aspects or embodiments of electronic controllers disclosedor used in combination with systems and methods herein. For example,aspects of controllers used for directing methods and operationsdescribed herein may be realized by the components of FIG. 19.

In the schematic illustration of FIG. 19, a display portion 1912 andnonvolatile memory 1920 are coupled to a bus 1922 that is also coupledto random access memory (“RAM”) 1924, a processing portion (whichincludes N processing components) 1926, a field programmable gate array(FPGA) 1927, and a transceiver component 1928 that includes Ntransceivers.

Although the components depicted in FIG. 19 represent physicalcomponents, FIG. 19 is not intended to be a detailed hardware diagram;thus, many of the components depicted in FIG. 19 may be realized bycommon constructs or distributed among additional physical components.Some components of FIG. 19 may be omitted in some implementations.Moreover, it is contemplated that other existing and yet-to-be developedphysical components and architectures may be utilized to implement thefunctional components described with reference to FIG. 19.

The display portion 1912 may operate to provide a user interface for anoperator of the systems described herein. The display may be realized,for example, by a liquid crystal display, AMOLED display, or others, andin some implementations, the display may be realized by a touchscreendisplay to enable an operator to modify control aspects and to viewoperating parameter-values (e.g., cell or stack current, cell or stackvoltage, reactive power, operating trends, flow rates, pressures, etc.)of the disclosed electrochemical systems. In general, the nonvolatilememory 1920 may be a non-transitory memory that functions to store(e.g., persistently store) data and processor executable code, includingexecutable code that is associated with effectuating the methodsdescribed herein. In some embodiments, the nonvolatile memory 1920 mayinclude bootloader code, operating system code, file system code, andnon-transitory processor-executable code to facilitate the execution ofthe functionality of the logic and control components described herein.

In some implementations, the nonvolatile memory 1920 may be realized byflash memory (e.g., NAND or ONENAND memory), but it is contemplated thatother memory types may also be utilized. Although it may be possible toexecute the code from the nonvolatile memory 1920, the executable codein the nonvolatile memory may typically be loaded into RAM 1924 andexecuted by one or more of the N processing components in the processingportion 1926.

The N processing components in connection with RAM 1924 may generallyoperate to execute the instructions stored in nonvolatile memory 1920 tofacilitate execution of the methods disclosed herein. For example,non-transitory processor-executable instructions to effectuate aspectsof the methods described herein may be persistently stored innonvolatile memory 1920 and executed by the N processing components inconnection with RAM 1924. As one of ordinarily skill in the art willappreciate, the processing portion 1926 may include a video processor,digital signal processor (DSP), graphics processing unit (GPU), andother processing components.

In addition, or in the alternative, the FPGA 1927 may be configured toeffectuate one or more aspects of the methodologies described herein.For example, non-transitory FPGA-configuration-instructions may bepersistently stored in nonvolatile memory 1920 and accessed by the FPGA1927 (e.g., during boot up) to configure the FPGA 1927 to effectuate oneor more functions of the control and logic components described herein.

As one of ordinary skill in the art in view of this disclosure willappreciate, the depicted input and output modules may be used forseveral different purposes. Sensors, for example, may be coupled to theinput module, and the output module may generate control signals foroperating any of the various electrical, electronic, orelectro-mechanical components described herein.

The depicted transceiver component 1928 may include N transceiverchains, which may be used for communicating with external devices viawireless or wireline networks. Each of the N transceiver chains mayrepresent a transceiver associated with a particular communicationscheme (e.g., SCADA, DNP3, WiFi, Ethernet, Modbus, CDMA, Bluetooth, NFC,etc.).

Terminology Used

Although many of the examples and embodiments herein are described withreference to water electrolyzers, the same general structures, systems,and methods may be applied to other systems involving electrochemicalcell stacks such as fuel cells (in which gases are reacted to produceenergy) and flow batteries (in which energy is stored in the form of oneor more ionic species in an aqueous or non-aqueous solution).

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. Various modifications to the above embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, it is intended that the scope ofthe present invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

In particular, materials and manufacturing techniques may be employed aswithin the level of those with skill in the relevant art. Furthermore,reference to a singular item, includes the possibility that there areplural of the same items present. More specifically, as used herein andin the appended claims, the singular forms “a,” “and,” “said,” and “the”include plural referents unless the context clearly dictates otherwise.As used herein, unless explicitly stated otherwise, the term “or” isinclusive of all presented alternatives, and means essentially the sameas the phrase “and/or.” It is further noted that the claims may bedrafted to exclude any optional element. As such, this statement isintended to serve as antecedent basis for use of such exclusiveterminology as “solely,” “only” and the like in connection with therecitation of claim elements, or use of a “negative” limitation. Unlessdefined otherwise herein, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs.

ADDITIONAL EMBODIMENTS

Additional embodiments may include:

Embodiment 1. An electrochemical system comprising: a stack of confinedelectrolyte electrochemical cells, each individual electrochemical cellindependently comprising: a first half-cell chamber containing a firstvolume of electrolyte in contact with a first electrode; a secondhalf-cell chamber in contact with a counter-electrode; a separatorseparating the first half-cell chamber from the second half-cellchamber; and a first electrolyte capture-and-return system incommunication with the first half-cell, the electrolytecapture-and-return system configured to capture electrolyte from thefirst volume of electrolyte that is escaping the first half-cell chamberand to drive the captured electrolyte back into at least one of thefirst half-cell chamber and the second half-cell chamber via anelectrolyte return conduit.

Embodiment 2. The electrochemical system of Embodiment 1, whereinelectrolyte in each individual electrochemical cell of the stack isfluidically isolated from electrolyte in each other individualelectrochemical cell of the stack.

Embodiment 3. The electrochemical system of Embodiment 1 or 2, whereinthe first electrolyte capture-and-return system fluidically isolatescaptured electrolyte from fluid communication with electrolyte in anyother cell of the cell-stack.

Embodiment 4. The electrochemical system of any of Embodiments 1-3further comprising a second electrolyte capture-and-return system incommunication with the second half-cell chamber; wherein the secondhalf-cell chamber comprises a second volume of electrolyte; and whereinthe second electrolyte capture-and-return system is configured tocapture electrolyte from the second volume of electrolyte that isescaping the second half-cell chamber and to drive the capturedelectrolyte back into the first half-cell chamber, the second half-cellchamber or both.

Embodiment 5. The electrochemical system of any of Embodiments 1-4,wherein each of the first electrolyte capture-and-return system and/orsecond electrolyte capture-and-return system independently comprises aliquid-gas separation chamber, the liquid-gas separation chamber beingunique to the respective individual electrochemical cell in which theyreside. Embodiment 5b: The electrochemical system of any of Embodiments1-4, wherein each of the first electrolyte capture-and-return systemcomprises a liquid-gas separation chamber, the liquid-gas separationchamber being unique to the respective individual electrochemical cellin which they reside.

Embodiment 6. The electrochemical system of any of Embodiments 1-5,wherein the first electrolyte capture-and-return system is in fluidcommunication with a first gas removal manifold and/or the secondelectrolyte capture-and-return system is in fluid communication with asecond gas removal manifold; and wherein the each of the first gasremoval manifold and the second gas removal manifold, if present, is influid communication with each of the electrochemical cells in the stack.Embodiment 6b: the electrochemical system of any of Embodiments 1-5,wherein the first electrolyte capture-and-return system is in fluidcommunication with a first gas removal manifold; and wherein the firstgas removal manifold is in fluid communication with each of theelectrochemical cells in the stack.

Embodiment 7. The electrochemical system of Embodiment 6, wherein thefirst gas removal manifold and/or the second gas removal manifoldcontains a gas-removal liquid. Embodiment 7b: The electrochemical systemof Embodiment 6, wherein the first gas removal manifold contains agas-removal liquid.

Embodiment 8. The electrochemical system of Embodiment 7, wherein thegas-removal liquid is maintained within a pre-determined range of fluidpressure.

Embodiment 9. The electrochemical system of Embodiment 7 or 8, whereinthe gas-removal liquid is a non-conductive liquid.

Embodiment 10. The electrochemical system of any of Embodiments 1-9,further comprising a first fluid escape element through which gas andliquid electrolyte escapes the first half-cell chamber into the firstelectrolyte capture-and-return system and/or a second fluid escapeelement through which gas and liquid electrolyte escapes the secondhalf-cell chamber into the second electrolyte capture-and-return system,if present. Embodiment 10b: The electrochemical system of any ofEmbodiments 1-9, further comprising a first fluid escape element throughwhich gas and liquid electrolyte escapes the first half-cell chamberinto the first electrolyte capture-and-return system.

Embodiment 11. The electrochemical cell of Embodiment 10, wherein thefluid escape element is a series fluid escape element characterized by apressure-drop of at least 0.1 bar.

Embodiment 12. The electrochemical system of any of Embodiments 1-11,wherein the first electrolyte capture-and-return system comprises afirst liquid-gas separator unique to the first half-cell and/or whereinthe second electrolyte capture-and-return system comprises a secondliquid-gas separator unique to the second half-cell. Embodiment 12b: Theelectrochemical system of any of Embodiments 1-11, wherein the firstelectrolyte capture-and-return system comprises a first liquid-gasseparator unique to the first half-cell.

Embodiment 13. The electrochemical system of Embodiment 12, wherein thefirst liquid-gas separator and/or second liquid-gas separator iscontained within a cell-frame and comprises at least two chambers joinedin fluid communication with one another. Embodiment 13b: Theelectrochemical system of Embodiment 12, wherein the first liquid-gasseparator is contained within a cell-frame and comprises at least twochambers joined in fluid communication with one another.

Embodiment 14. The electrochemical system of any of Embodiments 12-13,wherein each cell comprises a first one-way valve between the firstliquid-gas separator and the first gas removal manifold and/or each cellcomprises a second one-way valve between the second liquid-gas separatorand the second gas removal manifold; wherein the first one-way valve isoriented to allow flow of gas from the first liquid-gas separator intothe first gas removal manifold when gas pressure in the first liquid-gasseparator exceeds a fluid pressure in the first gas removal manifold;and wherein the second one-way valve is oriented to allow flow of gasfrom the second liquid-gas separator into the second gas removalmanifold when gas pressure in the second liquid-gas separator exceeds afluid pressure in the second gas removal manifold. Embodiment 14b: Theelectrochemical system of any of Embodiments 12-13, wherein each cellcomprises a first one-way valve between the first liquid-gas separatorand the first gas removal manifold; wherein the first one-way valve isoriented to allow flow of gas from the first liquid-gas separator intothe first gas removal manifold when gas pressure in the first liquid-gasseparator exceeds a fluid pressure in the first gas removal manifold.

Embodiment 15. The electrochemical system of any of Embodiments 1-14,wherein the first electrolyte capture-and-return system and/or thesecond electrolyte capture-and-return system comprises a membrane topromote the flow of product gas while maintaining electrolyte in therespective electrolyte capture-and-return system. Embodiment 15b: Theelectrochemical system of any of Embodiments 1-14, wherein the firstelectrolyte capture-and-return system comprises a membrane to promotethe flow of product gas while maintaining electrolyte in the firstelectrolyte capture-and-return system.

Embodiment 16. The electrochemical system of any of Embodiments 1-15,wherein the first electrolyte capture-and-return system and/or thesecond electrolyte capture-and-return system comprises one or more pumpsconfigured to return respectively captured electrolyte to the firsthalf-cell chamber or the second half-cell chamber, respectively.Embodiment 16b: The electrochemical system of any of Embodiments 1-15,wherein the first electrolyte capture-and-return system comprises one ormore pumps configured to return captured electrolyte to the firsthalf-cell chamber.

Embodiment 17. The electrochemical system of any of Embodiments 1-16,wherein the first electrolyte capture-and-return system and/or thesecond electrolyte capture-and-return system is configured to allow formixing of the electrolyte. Embodiment 17b: The electrochemical system ofany of Embodiments 1-16, wherein the first electrolytecapture-and-return system is configured to allow for mixing of theelectrolyte.

Embodiment 18. The electrochemical system of any of Embodiments 1-17,wherein the first electrolyte capture-and-return system and/or thesecond electrolyte capture-and-return system is configured to capture atleast 80% by mass of the electrolyte displaced from the respectivehalf-cell as a liquid, as a mist, or as a combination thereof.Embodiment 18b: The electrochemical system of any of Embodiments 1-17,wherein the first electrolyte capture-and-return system is configured tocapture at least 80% by mass of the electrolyte displaced from therespective half-cell as a liquid, as a mist, or as a combinationthereof.

Embodiment 19. The electrochemical system of any of Embodiments 1-18,wherein the electrochemical system is a battery, a flow battery or afuel cell.

Embodiment 20. The electrochemical system of any of Embodiments 1-19,wherein the electrochemical system is an alkaline electrolysis cell.

Embodiment 21. The electrochemical system of any of Embodiments 1-20,wherein the electrochemical cell generates hydrogen gas and oxygen gasas product gasses.

Embodiment 22. The electrochemical system of Embodiment 21, wherein theseparator is a proton exchange membrane (PEM) or an anion exchangemembrane (AEM), and wherein the electrolyte is deionized water.

Embodiment 23. The electrochemical system of Embodiment 20 or 21,wherein the electrolyte is an aqueous alkaline solution.

Embodiment 24. The electrochemical system of Embodiment 23, wherein theelectrolyte comprises potassium hydroxide, sodium hydroxide, lithiumhydroxide or any combination thereof.

Embodiment 25. The electrochemical system of any of Embodiments 1-24,wherein each electrochemical cell of the stack further comprises anexpansion chamber unique to the respective electrochemical cell and influid communication with the first half-cell chamber and the secondhalf-cell chamber of the respective electrochemical cell, the expansionchamber having an expandable and contractible volume and beingconfigured to allow volumetric expansion of liquid and gas in one orboth of the half-cell chambers.

Embodiment 26. The electrochemical system of Embodiment 25, wherein theexpansion chamber is configured to reduce a pressure differentialbetween the first half-cell chamber and the second half-cell chamber viaan expansion and/or contraction of the expansion chamber's volume.

Embodiment 27. The electrochemical cell of Embodiment 25 or 26, whereinthe expansion chamber's volume changes based on a pressure in the firsthalf-cell chamber and a pressure in the second half-cell chamber.

Embodiment 28. The electrochemical system of any of Embodiments 25-27,wherein the expansion chamber is in fluid communication with firstelectrolyte capture-and-return system and the second electrolytecapture-and-return system, if present.

Embodiment 29. The electrochemical system of any of Embodiments 25-28,wherein each electrochemical cell of the stack further comprises anexpansion resistor in operable communication with the expansion chamber.

Embodiment 30. The electrochemical system of Embodiment 29, wherein theexpansion resistor is a spring, a bellow, a diaphragm, a balloon, avolume of working fluid maintained at a predetermined pressure, aphysical property of the expansion chamber or any combination thereof.

Embodiment 31. The electrochemical system of any of Embodiments 25-30,wherein the expansion chamber comprises a divider to maintain separationof first volume of electrolyte from the first half-cell chamber andsecond volume of electrolyte from the second half-cell chamber.

Embodiment 32. The electrochemical system of any of Embodiments 1-31,wherein the electrochemical cell further comprises a make-up liquidsupply in fluid communication with the electrochemical cell to providemake-up liquid to the first half-cell, the second half-cell, or both.

Embodiment 33. The electrochemical system of Embodiment 32 furthercomprising a one-way valve positioned between the make-up liquid supplyand the electrochemical cell, the one-way valve arranged to allow fluidflow into but not out of the electrochemical cell.

Embodiment 34. The electrochemical system of Embodiment 32 or 33,wherein the make-up liquid is provided to the electrochemical cell by asupply manifold and wherein the supply manifold is in fluidcommunication with each electrochemical cell in the stack.

Embodiment 35. The electrochemical system of Embodiment 34, wherein theone-way valve regulates the flow of make-up liquid into theelectrochemical cell based on a pressure difference between the supplymanifold and the electrochemical cell.

36. The electrochemical system of Embodiment 35, wherein the one-wayvalve regulates the flow of make-up liquid into the electrochemical cellbased only on the pressure difference between the supply manifold andthe electrochemical cell.

Embodiment 37. The electrochemical system of any of Embodiments 32-36,wherein the make-up liquid is deionized water.

Embodiment 38. The electrochemical system of any of Embodiments-37further comprising a pump operably connected to each of theelectrochemical cells and arranged to drive captured electrolyte intoone or both of the half-cell chambers.

Embodiment 39. The electrochemical system of any of Embodiments 12-38further comprising a pump operably connected to each of theelectrochemical cells and arranged to drive captured electrolyte fromthe liquid-gas separator into one or both of the half-cell chambers.

Embodiment 40. The electrochemical system of Embodiment 38 or 37,wherein the pump is a ventricular pump or a positive displacement pump.

Embodiment 41. The electrochemical system of any of Embodiments 38-40,wherein the pump is capable of driving both liquid and gas through theelectrolyte return channel.

Embodiment 42. The electrochemical system of any of Embodiments 1-41,wherein the stack is arranged in a prismatic layered configuration, acylindrical stack of circular cell-frames, a spiral jellyrollconfiguration, a prismatic jellyroll configuration or any other rolledjellyroll or stacked prismatic configuration.

Embodiment 43. The electrochemical system of any of Embodiments 1-42,wherein the second half-cell chamber comprises a product gas generatedin the second half-cell chamber and wherein the second half-cell chamberis free of electrolyte during operation of the electrochemical system.

Embodiment 44. The electrochemical system of Embodiment 43, wherein eachelectrochemical cell comprises a gas-injector manifold configured tomaintain a gas pressure in the second half-cell chamber sufficient toprevent a liquid electrolyte from entering the second half-cell chamber.

Embodiment 45. The electrochemical system of Embodiment 44, whereingas-injector manifold injects a second gas into the second half-cellchamber.

Embodiment 46. The electrochemical system of Embodiment 45, wherein thesecond gas is different from the product gas.

Embodiment 47. The electrochemical system of Embodiments 43-46, whereinthe electrochemical system is configured such that product gas from thesecond half-cell chamber of each electrochemical cell is used to coolthe electrochemical cells in the stack.

Embodiment 48. The electrochemical cell of Embodiment 47, wherein thestack comprises one or more heat-exchangers that receive and cool theproduct gas; and wherein the product gas is injected into eachelectrochemical cell via a gas-injector manifold after the product gasis cooled via the one or more heat exchangers.

Embodiment 49. The electrochemical cell of any of Embodiments 1-48,wherein the stack is a bipolar stack.

Embodiment 50. The electrochemical system of any of Embodiments 1-48,wherein the stack is a bipolar stack comprising bipolar plates betweenadjacent cells, and wherein each bipolar plate comprises a flow channellayer sandwiched between first and second outer layers, the flow channellayer defining one or more coolant flow channels and the flow channellayer being sealed to the first and second outer layers.

Embodiment 51. An electrochemical system, comprising: a stack ofelectrochemical cells, each individual electrochemical cellindependently comprising: a first half-cell chamber containing a firstelectrode and containing a volume of fluid fluctuating between a firstfluid pressure and a second fluid pressure; a second half-cell chambercontaining a second electrode; a separator separating the firsthalf-cell chamber from the second half-cell chamber; and a make-upliquid inlet comprising a one-way valve arranged to provide flow ofmake-up liquid into the first half-cell chamber and to prevent flow ofliquid out of the half-cell through the make-up liquid inlet; a make-upliquid supply manifold in fluid communication with the make-up liquidinlet of all cells of the stack, the make-up liquid supply manifoldcontaining a make-up liquid at a third fluid pressure, the third fluidpressure is a controlled pressure that is greater than the firstpressure and less than the second pressure. In some embodiments, thevolume of fluid can be a mixture of gas and liquid. In some embodiments,the controlled pressure is controlled by an electromechanical regulatorwhich can be operated or controlled by an electronic controller.

Embodiment 52. The electrochemical system of Embodiment 51, wherein thethird pressure is within 0.5±0.2 bar of an average steady-stateoperating pressure of the volume of fluid in the first half-cellchamber.

Embodiment 53. The electrochemical system of Embodiment 51, wherein anelectrolyte in each individual electrochemical cell of the stack isfluidically isolated from an electrolyte in each other individualelectrochemical cell of the stack.

Embodiment 54. A method of operating an electrochemical system; whereinthe electrochemical system comprises: a stack of electrochemical cells,each individual electrochemical cell independently comprising: a firsthalf-cell chamber containing a first electrode and containing a volumeof fluid fluctuating between a first fluid pressure and a second fluidpressure; a second half-cell chamber containing a second electrode; aseparator separating the first half-cell chamber from the secondhalf-cell chamber; and a make-up liquid inlet comprising a one-wayvalve; and a make-up liquid supply manifold in fluid communication withthe make-up liquid inlet of all cells of the stack, the make-up liquidsupply manifold containing a make-up liquid at a third fluid pressure;and the method comprising steps of: providing, via the one-way valve, aflow of make-up liquid into the first half-cell chamber; preventing, viathe one-way vale, a flow of liquid out of the half-cell through themake-up liquid inlet; and controlling the third fluid pressure such thatit is greater than the first pressure and less than the second pressure.In some embodiments, the volume of fluid can be a mixture of gas andliquid, for example.

Embodiment 55. The method of Embodiment 54, wherein an electrolyte ineach individual electrochemical cell of the stack is fluidicallyisolated from an electrolyte in each other individual electrochemicalcell of the stack.

Embodiment 56. An electrochemical system comprising: a stack ofelectrochemical cells, each individual electrochemical cellindependently comprising: a first half-cell chamber containing a firstvolume of liquid in contact with a first electrode; a second half-cellchamber comprising a counter-electrode; a separator membrane separatingthe first half-cell chamber from the second half-cell chamber; a firstliquid-gas separator outside of the first half-cell chamber and in fluidcommunication with the first half-cell chamber via a first fluid escapeelement; and a first pump arranged to drive liquid from the firstliquid-gas separator into the first half-cell chamber via a liquidreturn channel that is separate from the fluid escape element. In someembodiments, the liquid is deionized water.

Embodiment 57. The electrochemical system of Embodiment 56, wherein anelectrolyte in each individual electrochemical cell of the stack isfluidically isolated from an electrolyte in each other individualelectrochemical cell of the stack.

Embodiment 58. The electrochemical cell of Embodiment 56 or 57, whereinthe second half-cell chamber further comprises a second volume ofliquid.

Embodiment 59. The electrochemical system of any of Embodiments 56-58,wherein the pump is a planar ventricular pump.

Embodiment 60. The electrochemical system of any of Embodiments 56-59,wherein each individual cell independently further comprises anexpansion volume in fluid communication with the first half-cellchamber.

Embodiment 61. An electrochemical system comprising: a bipolar stack ofelectrochemical cells in which adjacent cells share a bipolar platebetween them, each individual electrochemical cell independentlycomprising: a first half-cell chamber containing a first electrode; afirst electrically conductive egress channel joining the first half-cellto a first drip chamber, an electrically non-conductive gap between anoutlet end of the first egress channel and the first drip chamber; asecond half-cell chamber containing a second electrode; a secondelectrically conductive egress channel joining the second half-cell to asecond drip chamber, an electrically non-conductive gap between anoutlet end of the second egress channel and the second drip chamber; aseparator membrane separating the first half-cell chamber from thesecond half-cell chamber; a first electrical lead joined to a bipolarplate; a second electrical lead joined to the first drip-chamber; and athird electrical lead joined to the second drip chamber; and anelectronic controller configured to monitor electric potential, current,or voltage between pairs of the first electrical lead, the secondelectrical lead, and the second electrical lead.

Embodiment 62. The electrochemical system of Embodiment 61, wherein anelectrolyte in each individual electrochemical cell of the stack isfluidically isolated from an electrolyte in each other individualelectrochemical cell of the stack.

Embodiment 63. An electrochemical system comprising: at least oneconfined electrolyte electrochemical cell comprising: the electrolyte; afirst half-cell comprising a first electrode in contact with a firstvolume of the electrolyte and a first electrolyte capture-and-returnsystem; a second half-cell comprising a second electrode in contact witha second volume of the electrolyte and a second electrolytecapture-and-return system; and a separator separating the firsthalf-cell from the second half-cell; wherein the first electrolytecapture-and-return system is configured to capture electrolyte escapingfrom the first half-cell and return at least a portion of the capturedelectrolyte to the first half-cell without mixing it with electrolytefrom any other cell; and wherein the second electrolytecapture-and-return system is configured to capture electrolyte escapingfrom the second half-cell and return at least a portion of the capturedelectrolyte to the second half-cell without mixing it with electrolytefrom any other cell.

Embodiment 64. The electrochemical system of Embodiment 63, wherein thefirst electrolyte capture-and-return system is fluidically isolated fromthe second half-cell and wherein the second electrolytecapture-and-return system is fluidically isolated from the firsthalf-cell.

Embodiment 65. The electrochemical system of Embodiment 63 or 64,wherein electrolyte in each individual electrochemical cell of the stackis fluidically isolated from electrolyte in each other individualelectrochemical cell of the stack.

Embodiment 66. The electrochemical system of Embodiment 65, wherein eachof the first and second electrolyte capture-and-return systemsindependently fluidically isolate respective captured electrolyte fromfluid communication with electrolyte in any other cell of thecell-stack.

Embodiment 67. A method of generating at least one product gascomprising: providing an electrochemical system comprising: at least oneelectrochemical cell comprising: an electrolyte; a first half-cellhaving a first electrode in communication with a first volume of theelectrolyte and a first electrolyte capture-and-return system; a secondhalf-cell including a second electrode in communication with a secondvolume of the electrolyte; and a separator separating the firsthalf-cell from the second half-cell; capturing electrolyte escaping fromthe first half-cell via a first electrolyte capture-and-return systemand returning the captured electrolyte to the first half-cell; andreacting the electrolyte in the at least one electrochemical cellthereby generating at least one product gas.

Embodiment 68. The method of Embodiment 67, wherein the second half-cellfurther comprises a second electrolyte capture-and-return system; andwherein the method further comprises capturing electrolyte escaping fromthe second half-cell via a second electrolyte capture-and-return systemand returning the captured electrolyte to the second half-cell.

Embodiment 69. The electrochemical system of Embodiment 68, wherein thefirst electrolyte capture-and-return system is fluidically isolated fromthe second half-cell and wherein the second electrolytecapture-and-return system is fluidically isolated from the firsthalf-cell.

Embodiment 70. The electrochemical system of any of Embodiments 67-69,wherein electrolyte in each individual electrochemical cell of the stackis fluidically isolated from electrolyte in each other individualelectrochemical cell of the stack.

Embodiment 70. A method for generating hydrogen and oxygen gascomprising: providing an electrolyzer comprising: a plurality ofelectrochemical cells each independently comprising: an aqueouselectrolyte; a first half-cell having a first electrode in communicationwith first portion of the aqueous electrolyte, a first electrolytecapture-and-return system and a first gas capture system; a secondhalf-cell including a second electrode in communication with a secondportion of the aqueous electrolyte and a second gas capture system; anda separator separating the first half-cell from the second half-cell;capturing electrolyte displaced from the first half-cell via a firstelectrolyte capture-and-return system and returning the electrolyte tothe first half-cell; and electrolyzing the aqueous electrolyte in eachof the electrochemical cells, thereby generating the first gas and thesecond gas, wherein each first gas capture system is in fluidcommunication with one another and each second gas capture system is influid communication with one another.

Embodiment 72. The method of Embodiment 71, wherein the second half-cellfurther comprises a second electrolyte capture-and-return system; andwherein the method further comprises capturing electrolyte displacedfrom the second half-cell via a second electrolyte capture-and-returnsystem and returning the electrolyte to the second half-cell.

Embodiment 73. The method of Embodiment 70 or 72, wherein the first gasis oxygen and the first gas capture system is an oxygen gas capturesystem or wherein the first gas is hydrogen and the first gas capturesystem is a hydrogen gas capture system.

Embodiment 74. The method of any of Embodiments 71-73, wherein the firstgas is oxygen and the first gas capture system is an oxygen gas capturesystem and wherein the second gas is hydrogen and the second gas capturesystem is a hydrogen gas capture system.

Embodiment 75. The method of any of Embodiments 71-74, wherein theseparator is a proton exchange membrane (PEM) or an anion exchangemembrane (AEM).

Embodiment 76. The method of any of Embodiments 71-75, wherein eachindividual electrochemical cell of the plurality of electrochemicalcells independently further comprises an expansion volume in fluidcommunication with the first half-cell and the second half-cell.

Embodiment 77. The method of any of Embodiments 71-76, wherein the firstelectrolyte capture-and-return system is in fluid communication with thesecond electrolyte capture-and-return system in each of theelectrochemical cells.

Embodiment 78. The method of any of Embodiments 71-76, wherein anyelectrolyte capture-and-return system of an individual electrochemicalcell is fluidically isolated from any electrolyte capture-and-returnsystem of each other electrochemical cell in the electrolyzer.

Embodiment 79. The method of any of Embodiments 71-78, whereinelectrolyte in each individual electrochemical cell of the stack isfluidically isolated from electrolyte in each other individualelectrochemical cell of the stack.

Embodiment 80. A ventricular pump comprising: a pump chamber containingan actuation fluid on a first side of a fluid driver, and a driven fluidon a second side of the fluid driver opposite the first side; anup-stream one-way valve arranged to allow flow through a driven fluidin-flow aperture into the pump chamber on the first side of the fluiddriver; a down-stream one-way valve arranged to allow flow through adriven fluid out-flow aperture from the pump chamber on the first sideof the fluid driver; an actuation fluid inlet in fluid communicationwith the pump chamber on the first side of the fluid driver; anactuation fluid in the actuation fluid inlet and in the pump chamber onthe first side of the fluid driver; and an actuator configured to applya compressive and/or expansive force to the actuation fluid sufficientto at least partially deflect the fluid driver.

Embodiment 81. The ventricular pump of Embodiment 80, wherein theactuation fluid is an incompressible liquid.

Embodiment 82. The ventricular pump of Embodiment 81, wherein theactuation fluid is a compressible gas.

Embodiment 83. The ventricular pump of Embodiment 80, wherein the pumpchamber is formed in a cell-frame of one of a plurality of cell-framesin a cell-stack.

Embodiment 84. The ventricular pump of Embodiment 83, wherein theactuation fluid inlet is in fluid communication with an actuation fluidmanifold extending through the cell-stack.

Embodiment 85. A method of operating an electrolyzer system comprising aplurality of electrochemical cells in a cell-stack, each cell comprisinga positive half-cell chamber separated from a negative half-cell chamberby a proton exchange membrane (PEM), the method comprising: flowing aprocess water into the positive half-cell chamber of eachelectrochemical cell in the cell-stack at a first rate not greater than1,000% of a second rate at which the process water is consumed in thepositive half-cell chamber by being split into hydrogen and oxygengases; flowing a coolant through one or more heat-exchangers in thecell-stack; withdrawing gas from the negative half-cell chamber of eachelectrochemical cell via a negative gas removal manifold; maintainingthe negative gas removal manifold at a pressure of at least 10 barabsolute pressure; and withdrawing a mixture of oxygen gas and liquidprocess water from the positive half-cell chamber of eachelectrochemical cell through a common outlet in the positive half-cellchamber of each electrochemical cell.

Embodiment 86. The method of Embodiment 85, further comprisingregulating a first fluid pressure in a supply manifold directingprocesses water into the cell-stack.

Embodiment 87. The method of Embodiment 86, further comprisingregulating a second fluid pressure in a fluid removal manifold throughwhich the mixture of oxygen gas and process water is removed frompositive half-cells of the cell-stack.

Embodiment 88. The method of any one of Embodiments 85-87, wherein eachof the one or more heat exchangers in the cell-stack comprises one ormore flow channels within bipolar plate structures between adjacentelectrochemical cells.

Embodiment 89. The method of Embodiment 88, wherein each bipolar platestructure comprises a flow channel layer sandwiched between first andsecond outer layers, the flow channel layer defining one or more coolantflow channels and being sealed to the first and second outer layers.

Embodiment 90. The method of Embodiment 85, further comprisingwithdrawing process water from the cell stack and comprising returningprocess water to the cell stack; wherein process water withdrawn fromthe cell-stack is not directed through a heat exchanger after thecell-stack and before being returned to the cell-stack.

Embodiment 91. The method of any one of Embodiments 85-90, wherein eachelectrochemical cell in the cell-stack comprises an expansion chamber influid communication with the positive half-cell chamber.

Embodiment 92. A method of operating an electrolyzer system comprising aplurality of electrochemical cells in a cell-stack, each cell comprisinga positive half-cell chamber separated from a negative half-cell chamberby an anion exchange membrane (AEM), the method comprising: flowing aprocess water into the negative half-cell chamber of eachelectrochemical cell in the cell-stack at a first rate not greater than1,000% of a second rate at which the process water is consumed in thenegative half-cell chamber of each electrochemical cell by being splitinto hydrogen and oxygen gases; flowing coolant through one or moreheat-exchangers in the cell-stack; withdrawing gas from the positivehalf-cell chamber of each electrochemical cell via a positive gasremoval manifold; maintaining the negative half-cell chamber of eachelectrochemical cell at a fluid pressure of at least 10 bar absolutepressure; and withdrawing a mixture of hydrogen gas and liquid processwater from the negative half-cell chamber of each electrochemical cellthrough a common outlet in the negative half-cell chamber of eachelectrochemical cell.

Embodiment 93. The method of Embodiment 92, further comprisingregulating a first fluid pressure in a supply manifold directingprocesses water into the cell-stack.

Embodiment 94. The method of Embodiment 93, further comprisingregulating a second fluid pressure in a fluid removal manifold throughwhich the mixture of oxygen gas and process water is removed frompositive half-cells of the cell-stack.

Embodiment 95. The method of any one of Embodiments 92-94, wherein eachof the one or more heat exchangers in the cell-stack comprises one ormore flow channels within bipolar plate structures between adjacentcells.

Embodiment 96. The method of Embodiment 95, wherein each bipolar platestructure comprises a flow channel layer sandwiched between first andsecond outer layers, the flow channel layer defining one or more coolantflow channels and being sealed to the first and second outer layers.

Embodiment 97. The method of any one of Embodiments 92-95, furthercomprising withdrawing process water from the cell stack and comprisingreturning process water to the cell stack; wherein process waterwithdrawn from the cell-stack is not directed through a heat exchangerafter the cell-stack and before being returned to the cell-stack.

Embodiment 98. The method of any one of Embodiments 92-97, wherein eachelectrochemical cell in the cell-stack comprises an expansion chamber influid communication with the positive half-cell chamber.

Embodiment 99. A water electrolyzer system, comprising: a cell-stackcomprising a plurality of electrochemical cells, each cell comprising apositive half-cell chamber separated from a negative half-cell chamberby an anion exchange membrane (AEM); each negative half-cell chambercomprising a fluid exit having a fluid escape element configured toallow egress of a mixed-flow of hydrogen gas and water; a negative fluidremoval manifold in communication with the negative half-cell chamber ofeach electrochemical cell in the cell-stack, the negative fluid removalmanifold containing a mixture of hydrogen and water at a first regulatedfluid pressure; a supply manifold configured to deliver process water tothe negative half-cell chamber of each electrochemical cell in thecell-stack, wherein the process water in the supply manifold is at asecond regulated fluid pressure that is greater than the first regulatedfluid pressure; and a positive fluid removal manifold in communicationwith each positive half-cell chamber of the cell-stack, the positivefluid removal manifold containing oxygen gas at a third fluid pressure.

Embodiment 100. The system of Embodiment 99, further comprising at leastone bipolar plate heat exchanger between adjacent cells in thecell-stack, each bipolar plate heat exchanger comprising a coolantchannel between electrically conductive outer layers.

Embodiment 101. The system of any one of Embodiments 99-100, furthercomprising a gas-liquid separator downstream of the negative fluidremoval manifold, and the system comprising a conduit directing waterfrom the gas-liquid separator to the supply manifold, and wherein noheat exchanger is present between the negative fluid removal manifoldand the supply manifold.

Embodiment 102. The system of Embodiment 101, wherein the gas-liquidseparator comprises a gas pocket region above a liquid-level in agas-liquid separation chamber.

Embodiment 103. The system of any one of Embodiments 99-102, furthercomprising an expansion chamber in fluid communication with the negativehalf-cell chamber of each cell.

Embodiment 104. The system of any one of Embodiments 99-103, furthercomprising a stack-bypass conduit directing a quantity of process waterfrom the supply manifold to the negative fluid removal manifold.

Embodiment 105. The system of any one of Embodiments 99-104, wherein atleast one of the fluid escape elements comprise one or more egresschannels configured to impart a non-linear flow resistance to the mixedfluid exiting the negative half-cell chambers.

Embodiment 106. The system of any one of Embodiments 99-10005, whereinat least one of the fluid escape elements comprise one or morephase-discriminating membranes.

Embodiment 107. A water electrolyzer system, comprising: a cell-stackcomprising a plurality of electrochemical cells, each cell comprising apositive half-cell chamber separated from a negative half-cell chamberby a proton exchange membrane (PEM); each positive half-cell chambercomprising a fluid exit having a fluid escape element configured toallow egress of a mixed-flow of oxygen gas and water; a positive fluidremoval manifold in communication with the positive half-cell chamber ofeach electrochemical cell in the cell-stack, the positive fluid removalmanifold containing a mixture of oxygen and water at a first regulatedfluid pressure; a supply manifold configured to deliver process water tothe positive half-cell chamber of each electrochemical cell in thecell-stack, wherein the process water in the supply manifold is at asecond regulated fluid pressure that is greater than the first regulatedfluid pressure; and a negative fluid removal manifold in communicationwith the negative half-cell chamber of each electrochemical cell in thecell-stack, the negative fluid removal manifold containing hydrogen gasat a third regulated fluid pressure that is greater than the secondfluid pressure.

Embodiment 108. The system of Embodiment 107, further comprising atleast one bipolar plate heat exchanger between adjacent cells in thecell-stack, each bipolar plate heat exchanger comprising a coolantchannel between electrically conductive outer layers.

Embodiment 109. The system of any one of Embodiments 107-108, furthercomprising a gas-liquid separator downstream of the positive fluidremoval manifold, and the system comprising a conduit directing waterfrom the gas-liquid separator to the supply manifold, and wherein noheat exchanger is present between the positive fluid removal manifoldand the supply manifold.

Embodiment 110. The system of any one of Embodiments 107-109, furthercomprising an expansion chamber in fluid communication with the positivehalf-cell chamber of each electrochemical cell.

Embodiment 111. The system of any one of Embodiments 107-110, furthercomprising a stack-bypass conduit directing a quantity of process waterfrom the supply manifold to the positive fluid removal manifold.

Embodiment 112. The system of any one of Embodiments 107-111, whereineach fluid escape element comprises an egress channel configured toimpart a non-linear flow resistance to the mixed fluid exiting thenegative half-cell chambers.

Embodiment 113. The system of any one of Embodiments 107-112, whereineach fluid escape element comprises one or more phase-discriminatingmembranes.

Embodiment 114. The method of any one of Embodiments 85-91, wherein theoxygen gas in the positive half-cell chamber of each electrochemicalcell is formed in the positive half-cell chamber via consumption ofprocess water in the respective cell.

Embodiment 115. The method of any one of Embodiments 92-98, wherein thehydrogen gas in the negative half-cell chamber of each electrochemicalcell is formed in the negative half-cell chamber via consumption ofprocess water in the respective cell.

Embodiment 116. The system of any one of Embodiments 99-106, wherein thehydrogen gas in the negative fluid removal manifold is formed in thenegative half-cell chambers of the cell-stack and wherein the oxygen gasin the positive fluid removal manifold is formed in the positivehalf-cell chambers of the cell-stack via consumption of process water inthe plurality of electrochemical cells.

Embodiment 117. The method of any one of Embodiments 85-91, wherein saidnegative gas removal manifold withdraws only gas from the negativehalf-cell chamber of each electrochemical cell via.

Embodiment 118. The method of any one of Embodiments 92-98, wherein saidpositive gas removal manifold withdraws only gas from the positivehalf-cell chamber of each electrochemical cell.

Statements Regarding Incorporation by Reference and Variations

All references throughout this application, for example patent documentsincluding issued or granted patents or equivalents; patent applicationpublications; and non-patent literature documents or other sourcematerial; are hereby incorporated by reference herein in theirentireties.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof, but it isrecognized that various modifications are possible within the scope ofthe invention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments, exemplary embodiments and optional features, modificationand variation of the concepts herein disclosed may be resorted to bythose skilled in the art, and that such modifications and variations areconsidered to be within the scope of this invention as defined by theappended claims. The specific embodiments provided herein are examplesof useful embodiments of the present invention and it will be apparentto one skilled in the art that the present invention may be carried outusing a large number of variations of the devices, device components,methods steps set forth in the present description. As will be obviousto one of skill in the art, methods and devices useful for the presentmethods can include a large number of optional composition andprocessing elements and steps.

When a group of substituents is disclosed herein, it is understood thatall individual members of that group and all subgroups are disclosedseparately. When a Markush group or other grouping is used herein, allindividual members of the group and all combinations andsub-combinations possible of the group are intended to be individuallyincluded in the disclosure. Specific names of compounds are intended tobe exemplary, as it is known that one of ordinary skill in the art canname the same compounds differently.

Every formulation or combination of components described or exemplifiedherein can be used to practice the invention, unless otherwise stated.

Whenever a range is given in the specification, for example, atemperature range, a pressure range, or a composition or concentrationrange, all intermediate ranges and subranges, as well as all individualvalues included in the ranges given are intended to be included in thedisclosure. It will be understood that any subranges or individualvalues in a range or subrange that are included in the descriptionherein can be excluded from the claims herein.

All patents and publications mentioned in the specification areindicative of the levels of skill of those skilled in the art to whichthe invention pertains. References cited herein are incorporated byreference herein in their entirety to indicate the state of the art asof their publication or filing date and it is intended that thisinformation can be employed herein, if needed, to exclude specificembodiments that are in the prior art. For example, when composition ofmatter are claimed, it should be understood that compounds known andavailable in the art prior to Applicant's invention, including compoundsfor which an enabling disclosure is provided in the references citedherein, are not intended to be included in the composition of matterclaims herein.

As used herein, “comprising” is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps. As usedherein, “consisting of” excludes any element, step, or ingredient notspecified in the claim element. As used herein, “consisting essentiallyof” does not exclude materials or steps that do not materially affectthe basic and novel characteristics of the claim. In each instanceherein, any of the terms “comprising”, “consisting essentially of” and“consisting of” may be replaced with either of the other two terms. Theinvention illustratively described herein suitably may be practiced inthe absence of any element or elements, limitation or limitations whichis not specifically disclosed herein.

The term “and/or” is used herein, in the description and in the claims,to refer to a single element alone or any combination of elements fromthe list in which the term and/or appears. In other words, a listing oftwo or more elements having the term “and/or” is intended to coverembodiments having any of the individual elements alone or having anycombination of the listed elements. For example, the phrase “element Aand/or element B” is intended to cover embodiments having element Aalone, having element B alone, or having both elements A and B takentogether. For example, the phrase “element A, element B, and/or elementC” is intended to cover embodiments having element A alone, havingelement B alone, having element C alone, having elements A and B takentogether, having elements A and C taken together, having elements B andC taken together, or having elements A, B, and C taken together

One of ordinary skill in the art will appreciate that startingmaterials, biological materials, reagents, synthetic methods,purification methods, analytical methods, assay methods, and biologicalmethods other than those specifically exemplified can be employed in thepractice of the invention without resort to undue experimentation. Allart-known functional equivalents, of any such materials and methods areintended to be included in this invention. The terms and expressionswhich have been employed are used as terms of description and not oflimitation, and there is no intention that in the use of such terms andexpressions of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the invention claimed.Thus, it should be understood that although the present invention hasbeen specifically disclosed by preferred embodiments and optionalfeatures, modification and variation of the concepts herein disclosedmay be resorted to by those skilled in the art, and that suchmodifications and variations are considered to be within the scope ofthis invention as defined by the appended claims.

1-57. (canceled)
 58. An electrochemical system, comprising: a stack ofelectrochemical cells, each individual electrochemical cellindependently comprising: a first half-cell chamber containing a firstelectrode and containing a volume of fluid fluctuating between a firstfluid pressure and a second fluid pressure; a second half-cell chambercontaining a second electrode; a separator separating the firsthalf-cell chamber from the second half-cell chamber; and a make-upliquid inlet comprising a one-way valve arranged to provide flow ofmake-up liquid into the first half-cell chamber and to prevent flow ofliquid out of the half-cell through the make-up liquid inlet; a make-upliquid supply manifold in fluid communication with the make-up liquidinlet of all cells of the stack, the make-up liquid supply manifoldcontaining a make-up liquid at a third fluid pressure, the third fluidpressure is a controlled pressure that is greater than the firstpressure and less than the second pressure.
 59. The electrochemicalsystem of claim 58, further comprising a first gas-removal manifold influid communication with the first half-cell chamber, the firstgas-removal manifold containing a first gas-removal liquid flowingtherethrough and maintained at a controlled fourth pressure that is lessthan the first pressure.
 60. The electrochemical system of claim 59,further comprising a second gas-removal manifold in fluid communicationwith the second half-cell chamber, the second gas-removal manifoldcontaining a second gas-removal liquid flowing therethrough andmaintained at a controlled fifth pressure that is equal to the fourthpressure.
 61. The electrochemical system of claim 60, further comprisinga first fluid escape element between the first half-cell chamber and thefirst gas-removal manifold, wherein the first fluid escape elementimparts a resistance to flow of gas which dampens pressure oscillationsbetween the first half-cell chamber and the first gas-removal manifold.62. The electrochemical system of claim 61, further comprising a secondfluid escape element between the second half-cell chamber and the secondgas-removal manifold, wherein the second fluid escape element imparts aresistance to flow of gas which dampens pressure oscillations betweenthe second half-cell chamber and the second gas-removal manifold. 63.The electrochemical system of claim 62, wherein the first fluid escapeelement or the second fluid escape element is a series fluid escapeelement.
 64. The electrochemical system of claim 63, wherein the seriesfluid escape element is an egress channel with a total interior fluidpath length that is at least 10 times greater than an interiorcross-sectional area.
 65. The electrochemical system of claim 63,wherein the series fluid escape element is an egress channel with atortuous path.
 66. The electrochemical system of claim 63, wherein theseries fluid escape element is an egress channel with a mechanicallyrestricted conduit.
 67. The electrochemical system of claim 63, whereinincompressible liquid and compressible gas flow through the series fluidescape element as discrete liquid pockets of and gas pockets, whereinthe liquid pockets experience flow resistance due to surface tensionwith an interior wall of the fluid escape element.
 68. A method ofoperating an electrochemical system; wherein the electrochemical systemcomprises: a stack of electrochemical cells, each individualelectrochemical cell independently comprising: a first half-cell chambercontaining a first electrode and containing a volume of fluidfluctuating between a first fluid pressure and a second fluid pressure;a second half-cell chamber containing a second electrode; a separatorseparating the first half-cell chamber from the second half-cellchamber; and a make-up liquid inlet comprising a one-way valve; and amake-up liquid supply manifold in fluid communication with the make-upliquid inlet of all cells of the stack, the make-up liquid supplymanifold containing a make-up liquid at a third fluid pressure; and themethod comprising steps of: providing, via the one-way valve, a flow ofmake-up liquid into the first half-cell chamber; preventing, via theone-way vale, a flow of liquid out of the half-cell through the make-upliquid inlet; and controlling the third fluid pressure such that it isgreater than the first pressure and less than the second pressure. 69.The method of claim 68, further comprising removing a liquid-gas mixturefrom the first half-cell chamber, separating the mixture into firstliquid and first gas, and returning the first liquid to the half-cellwithout mixing the liquid with liquid from any other cell in the stack.70. The method of claim 69, further comprising removing the first gasvia a first gas-removal manifold common to all cells in the stack, andcontrolling a fluid pressure in the first gas-removal manifold at afourth pressure that is less than the first pressure.
 71. The method ofclaim 70, further comprising dampening pressure oscillations between thefirst half-cell chamber and the first gas-removal manifold.
 72. Themethod of claim 70, further comprising removing a second gas from thesecond half-cell chamber via a second gas-removal manifold common to allcells in the stack, and controlling a fluid pressure in the secondgas-removal manifold at a fifth pressure that is equal to the fourthpressure.
 73. The method of claim 72, further comprising dampeningpressure oscillations between the second half-cell chamber and thesecond gas-removal manifold.
 74. The electrochemical system of claim 58,wherein an electrolyte in each individual electrochemical cell of thestack is fluidically isolated from an electrolyte in each otherindividual electrochemical cell of the stack.
 75. The electrochemicalsystem of claim 58, wherein the volume of fluid is a mixture of gas andliquid.
 76. The electrochemical system of claim 58, wherein third fluidpressure is within 0.5±0.2 bar of an average steady-state operatingpressure of the volume of fluid in the first half-cell chamber.
 77. Theelectrochemical system of claim 58, wherein the second half-cell chamberfurther comprises a second volume of liquid.
 78. The electrochemicalsystem of claim 68, wherein an electrolyte in each individualelectrochemical cell of the stack is fluidically isolated from anelectrolyte in each other individual electrochemical cell of the stack.79. The electrochemical system of claim 68, wherein third fluid pressureis within 0.5±0.2 bar of an average steady-state operating pressure ofthe volume of fluid in the first half-cell chamber.
 80. Theelectrochemical system of claim 68, wherein the second half-cell chamberfurther comprises a second volume of liquid.